Absorbent articles with improved distribution properties under sur-saturation

ABSTRACT

An absorbent article contains at least one fluid storage member and at least one fluid distribution member. The fluid distribution member has an improved fluid handling property especially under sub-saturation conditions. Such members exhibit, at 50% of their saturation capacity, an increased permeability of at least about 14% of one at saturation. The fluid storage member has a higher Capillary Sorption Absorbency Height than the fluid distribution member.

GENERAL FIELD OF THE INVENTION

The present invention relates to hygienic absorbent articles, such asdisposable baby diapers, training pants, adult incontinence articles,feminine hygiene articles and the like, which comprise fluiddistribution members exhibiting an improved performance for distributingliquid within such articles.

BACKGROUND/PRIOR ART

In the general field of disposable absorbent articles and structures,materials exhibiting specific fluid distribution properties are wellknown. Such materials became more and more relevant with theintroduction of highly absorbent materials, also called AbsorbentGelling Materials or superabsorbent materials or shortly superabsorber,which do provide a good means for storing aqueous fluids such as urine,but do not enhance fluid transport, and even reduction of fluidtransport can occur, when, sub-optimal designs and/or suboptimalmaterials are employed, and phenomena often referred to as“gel-blocking” take place. For example, in structures where thesuperabsorbent is homogeneously mixed with cellulose fibers, a certaincritical concentration, which is strongly depending on the choice of thesuperabsorbent material, should not be exceeded in order to notdeteriorate efficacy of the absorbent core.

As a consequence, a vast number of absorbent core designs have appearedwith a separated functionality, such as by comprising not only liquidstorage regions or materials, but also regions with specializedproperties for enhanced acquisition and/or distribution of the fluid.Often, one region aimed at enhancing acquisition and distribution at thesame time.

Initially, the requirements for a distribution material were not veryhigh, and standard paper tissue materials such as used as wrapsheets inthe cores and described for example in U.S. Pat. No. 3,952,745 (Duncan),were applied to also enhance the fluid distribution, as described inEP-0 343 941 (Reising) or U.S. Pat. No. 4,578,068 (Kramer).

Further developments can be exemplified by EP-A-0,397,110 (Latimer)disclosing an absorbent article comprising a surge management portionfor improved fluid handling, having specific basis weights, acquisitiontimes and residual wetness; U.S. Pat. No. 4,898,642 (Moore et al.)discloses specially twisted, chemically stiffened cellulosic fibers andabsorbent structures made therefrom; EP-A-0,640,330 (Bewick-Sonntag etal.) discloses the use of such fibers in a specific arrangement withspecific superabsorbent materials.

Further approaches aimed at improving the wicking properties ofcellulose fiber based materials, such as U.S. Pat. Nos. 3,575,174 or4,781,710, whereby parts of the structure are compressed to a higherdensity, thus creating smaller pores for increased wicking height forexample along “wicking lines” or in closed mesh patterns.

As some of these materials did exhibit an undesired hard feel, methodsfor post formation treatments were well known to improve softness. “Postformation treatment” refers to the fact that—instead of or in additionto increasing softness during the making or formation of the tissue—thetissue is treated mechanically in a separate process step after formingand drying of the tissue, often just prior to further processing such ascombining the tissue with other materials to form an absorbent core orarticle. Examples for such treatments are U.S. Pat. No. 5,117,540(Walton) or U.S. Pat. No. 4,440,597 (Wells).

Other attempts to impact on the pore size of distribution materials isdescribed in U.S. Pat. No. 5,244,482 (Hassenboehler), aiming at reducingmaximum pore size by stretching a fibrous structure comprising meltablefibers in one direction and “freezing” the deformation by heat curing.

Also, special material composites were developed, aiming at a allowingto tailor the pore size and pore size distribution. Examples for suchimprovements are described in greater detail in U.S. Pat. No. 5,549,589(Homey et al.) or in PCT application WO 97/38654 (Seger et al.). Bothaim essentially at providing a resilient structure by using speciallystiffened cellulosic fibers such as crosslinked cellulose soft-woodfibers, and by filling the large pores with small and thin cellulosicfibers such as eucalyptus fibers. Both applications further add meansfor providing sufficient integrity and strength to the structure, thefirst one (U.S. Pat. No. 5,549,589) by adding thermoplastic fibers andpartially melt these, the second (WO 97/38654) by adding a chemicalbinder.

A further approach as disclosed in EP Application EP-A-0,810,078(d'Acchioli et al.) uses a special post-formation mechanical treatmentof webs, thereby imparting improved fluid handling properties such asdescribed by higher liquid flux rates at certain wicking heights.

With the wish to improve the functionality of the absorbent articles,more specific requirements for distribution materials developed, suchthat porous materials were investigated in more depth. In order toimprove the longitudinal fluid distribution, high surface area syntheticfibers were applied in absorbent structures, such as described in USStatuary Invention Registration H1511. Another class of materials arefoamed structures, such as cellulosic foams such as commerciallyavailable by Spontex SA, France.

Other polymeric foams for being used in absorbent articles weredisclosed in U.S. Pat. No. 5,268,224 (DesMarais), namely High InternalPhase polymerized materials, which can be used for storing liquids, andhave at the same time the ability to avoid localized saturation, byspreading the stored fluid throughout the material.

However, all these investigations so far aimed at improving the wickingproperties of the distribution materials such as flux, wicking heightand wicking times, but failed to recognize the importance of thedewatering mechanism of the distribution materials by the liquid storagematerials, especially when such materials are not fully saturated, suchas can be relevant in absorbent articles between multiple loadings.

OBJECTS OF THE INVENTION

Henceforth, it is an object of the present invention to provide improvedabsorbent articles having an improved dewatering functionality ofdistribution members, especially under low saturation conditions.

It is another object of the present invention, to provide improvedabsorbent articles comprising materials which allow liquid to betransported throughout an absorbent article even being saturated to alow or moderate degree of saturation.

It is a further object of the present invention to provide such articlesfurther comprising liquid storage materials having a good capillarysorption absorption performance.

SUMMARY

The present invention is an absorbent article containing a fluiddistribution member, which has a relatively high permeability even atsubsaturation conditions, and which has a lower Capillary SorptionAbsorption Height at 50% of its capacity at 0 cm, which is higher thanthe Capillary Soprtion Desorption Height at 50% of its capacity at 0 cmof a fluid storage member in liquid communication with this distributionmember in this article.

Thus, the distribution member has a permeability at 50% of itssaturation, which is at least more than about 14%, preferably more than18%, even more preferably more than 25% or even more than 35% of thepermeability at 100% saturation.

Thus, the first fluid storage member has as CSAH 50 of more than about15 cm, preferably of more than about 23 cm, even more preferably of morethan about 27 cm, or even more than about 30 cm, and most preferablymore than about 47 cm.

In a further preferred executions, the absorbent article comprises afluid distribution member which has a permeability at 30% of itssaturation k(30) which is more than about 3% of k(100), preferably morethan about 5%, more preferably even more than about 10% of k(100).

In further preferred embodiments, the fluid distribution member has aCSDH 50 value of less than about 150 cm, more preferably less than about100 cm, even more preferably less than about 75 cm, and most preferablyless than about 50 cm.

In a specific preferred execution, the fluid distribution membercomprises an open celled foam, which can expand upon wetting, and whichfurther can re-collapse upon loosing liquid. In a particularly preferredexecution, the distribution member comprises a hydrophilic, flexiblepolymeric foam structure of interconnected open-cells, even morepreferably of the HIPE type.

In a further execution, the absorbent article has at least two liquidstorage regions, whereby both liquid storage regions are in liquidcommunication with the fluid distribution member, wherein preferably atleast one of said liquid storage regions comprises material exhibiting aCapillary Sorption Absorption Height at 50% of its maximum capacity(CSAH 50) of at least about 40 cm.

In a further aspect of the invention, the absorbent article having suchdistribution member can be described by a crotch region and one or morewaist regions, whereby said crotch region has a lower ultimate fluidstorage capability than said one or more waist regions together, whichcan be described by having less than 0.9 times the average ultimatefluid storage basis capacity of the absorbent core, more preferably evenless than 0.5 times the average ultimate fluid storage basis capacity ofthe absorbent core, even more preferably less than 0.3 times the averageultimate fluid storage basis capacity of the absorbent core.

In a further aspect, the absorbent article has a crotch region having asectional ultimate fluid storage capacity of less than 49% of the totalcore ultimate fluid storage capacity, preferably less than 41% of thetotal core ultimate fluid storage capacity, even more preferably lessthan 23% the total core ultimate fluid storage capacity.

In an even further aspect of the present invention, the absorbentarticle has an ultimate liquid storage material providing at least 80%of the total ultimate storage capacity of the absorbent core, preferablymore than 90% of the total ultimate storage capacity of the absorbentcore.

In an even further aspect of the present invention, the absorbentarticle has very little liquid absorbent capacity in the crotch region,preferably at least 50% of the of the crotch region are containessentially no ultimate storage capacity.

Further, the absorbent article can have less than 50% of said ultimatestorage capacity positioned forwardly from the crotch zone in the fronthalf of the article, and more than 50% of said ultimate storage capacitypositioned in the rear half of the article. Even more preferably, theabsorbent article can have less than 33% of said ultimate storagecapacity positioned forwardly from the crotch zone in the front half ofthe article, and more than 67% of said ultimate storage capacity arepositioned in the rear half of the article.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 to 4 show different executions of the permeability test set up.FIGS. 1 and 2 relate to a simplified test. FIGS. 3 and 4 relate to ageneral test. FIGS. 1 and 3 relate to the measurement of the transplanarpermeability, and FIGS. 2 and 4 to the in-plane permeability.

FIG. 5—Shows the Capillary Sorption test stand (Capsorption)

FIG. 6—Shows a diaper as example for an absorbent article

DETAILED DESCRIPTION

As used herein, the term “fluid handling member” refers to thecomponents of the absorbent article that typically provide at least thefluid handling functionality. An absorbent article can comprise one ormore of the various fluid handling members, such as one or more fluidacquisition member, one or more fluid distribution members and/or one ormore fluid storage members. Each of these members can comprise on ormore sub-elements, which can be homogeneous or not, i.e. each member canbe made from one material or from several materials. For example, suchmembers can be layers, optionally consisting of sub-layers, and oroptionally having different composition, or density, or thickness.

Each of these members can have a specialized functionality, suchprimarily providing acquisition functionality or primarily providingfluid storage functionality. Alternatively, members can have multiplefunctionality, such as the very first “cellulose only” diapers whereinthe cellulose fluff performed acquisition, distribution and ultimatestorage functionality at the same time.

The “storage absorbent member” refers to the absorbent member(s) of theabsorbent core that function primarily to ultimately store absorbedfluids.

A “fluid distribution member” in the meaning of the present invention isa member, which satisfies the requirements as laid out for the fluiddistribution functionality, regardless whether the member also has someother fluid handling functionality.

A “fluid acquisition member” refers to parts or the absorbent core,which are primarily designed to receive the liquid as it reaches theabsorbent article.

As used herein, the term “absorbent core” refers to the members of theabsorbent article that are primarily responsible for fluid handling ofthe article, thus including the “fluid handling member(s)”. As such, theabsorbent core typically does not include the topsheet or backsheet ofthe absorbent article, though in certain instances the topsheet could beconsidered, for example, to provide specific fluid acquisitionperformance.

An absorbent core can be divided into “regions” of the core, whereinsuch “regions” can perform the functionality of one or more of themembers as outlined above. Thus, an acquisition region can comprise anacquisition member (and also comprise other members), it can consist ofan acquisition member (and nothing else), which can consist of anacquisition material. Or, an acquisition/distribution region cancomprise both an acquisition member and an distribution member.

As used herein, the term “absorbent articles” refers to devices whichabsorb and contain body exudates, and, more specifically, refers todevices which are placed against or in proximity to the body of thewearer to absorb and contain the various exudates discharged from thebody. As used herein, the term “body fluids” includes but is not limitedto urine, menses, vaginal discharges, sweat and feces.

The term “disposable” is used herein to describe absorbent articleswhich are not intended to be laundered or otherwise restored or reusedas an absorbent article (i.e., they are intended to be discarded afteruse and, preferably, to be recycled, composted or otherwise disposed ofin an environmentally compatible manner).

As used herein, the term “Z-dimension” refers to the dimensionorthogonal to the length and width of the member, core or article. TheZ-dimension usually corresponds to the thickness of the member, core orarticle. As used herein, the term “X-Y dimension” refers to the planeorthogonal to the thickness of the member, core or article. The X-Ydimension usually corresponds to the length and width, respectively, ofthe member, core or article.

As used herein, the terms “region(s)” or “zone(s)” refer to portions orsections of the absorbent member. Thereby, the region(s) or zone(s) canbe two-dimensional (front/back) or can be three-dimensional (like anacquisition region having—even if it were in the form of a layer—athree-dimensional extension).

As use herein, the term “layer” refers to an absorbent member whoseprimary dimension is X-Y, i.e., along its length and width. It should beunderstood that the term layer is not necessarily limited to singlelayers or sheets of material. Thus the layer can comprise laminates orcombinations of several sheets or webs of the requisite type ofmaterials. Accordingly, the term “layer” includes the terms “layers” and“layered”.

For purposes of this invention, the term “upper” should be understood torefers to absorbent members, such as layers, that are nearest to thewearer of the absorbent article, and typically face the topsheet of anabsorbent article; conversely, the term “lower” refers to absorbentmembers that are furthermost away from the wearer of the absorbentarticle and typically face the backsheet.

All percentages, ratios and proportions used herein are calculated byweight unless otherwise specified.

Absorbent Articles—General Description

An absorbent article generally comprises:

an absorbent core or core structure (which comprises the improved fluiddistribution members according to the present invention, and which mayconsist of sub-structures);

a fluid pervious topsheet;

a fluid impervious backsheet;

optionally further features like closure elements or elastification.

FIG. 6 is a plan view of an exemplary embodiment of an absorbent articleof the invention which is a diaper.

The diaper 20 is shown in FIG. 6 in its flat-out, uncontracted state(i.e. with elastic induced contraction pulled out except in the sidepanels wherein the elastic is left in its relaxed condition) withportions of the structure being cut-away to more clearly show theconstruction of the diaper 20 and with the portion of the diaper 20which faces away from the wearer, the outer surface 52, facing theviewer. As shown in FIG. 6, the diaper 20 comprises a containmentassembly 22 preferably comprising a liquid pervious topsheet 24, aliquid impervious backsheet 26 joined with the topsheet 24, and anabsorbent core 28 positioned between the topsheet 24 and the backsheet26; elasticized side panels 30; elasticized leg cuffs 32; an elasticwaist feature 34; and a closure system comprising a dual tensionfastening system generally multiply designated as 36. The dual tensionfastening system 36 preferably comprises a primary fastening system 38and a waist closure system 40. The primary fastening system 38preferably comprises a pair of securement members 42 and a landingmember 44. The waist closure system 40 is shown in FIG. 6 to preferablycomprise a pair of first attachment components 46 and a secondattachment component 48. The diaper 20 also preferably comprises apositioning patch 50 located subjacent each first attachment component46.

The diaper 20 is shown in FIG. 6 to have an outer surface 52 (facing theviewer in FIG. 6), an inner surface 54 opposed to the outer surface 52,a first waist region 56, a second waist region 58 opposed to the firstwaist region 56, and a periphery 60 which is defined by the outer edgesof the diaper 20 in which the longitudinal edges are designated 62 andthe end edges are designated 64. The inner surface 54 of the diaper 20comprises that portion of the diaper 20 which is positioned adjacent tothe wearer's body during use (i.e. the inner surface 54 generally isformed by at least a portion of the topsheet 24 and other componentsjoined to the topsheet 24). The outer surface 52 comprises that portionof the diaper 20 which is positioned away from the wearer's body (i.e.the outer surface 52 generally is formed by at least a portion of thebacksheet 26 and other components joined to the backsheet 26). The firstwaist region 56 and the second waist region 58 extend, respectively,from the end edges 64 of the periphery 60 to the lateral centreline 66of the diaper 20. The waist regions each comprise a central region 68and a pair of side panels which typically comprise the outer lateralportions of the waist regions. The side panels positioned in the firstwaist region 56 are designated 70 while the side panels in the secondwaist region 58 are designated 72. While it is not necessary that thepairs of side panels or each side panel be identical, they arepreferably mirror images one of the other. The side panels 72 positionedin the second waist region 58 can be elastically extensible in thelateral direction (i.e. elasticized side panels 30). (The lateraldirection (x direction or width) is defined as the direction parallel tothe lateral centreline 66 of the diaper 20; the longitudinal direction(y direction or length) being defined as the direction parallel to thelongitudinal centreline 67; and the axial direction (Z direction orthickness) being defined as the direction extending through thethickness of the diaper 20).

FIG. 6 shows a specific of the diaper 20 in which the topsheet 24 andthe backsheet 26 have length and width dimensions generally larger thanthose of the absorbent core 28. The topsheet 24 and the backsheet 26extend beyond the edges of the absorbent core 28 to thereby form theperiphery 60 of the diaper 20. The periphery 60 defines the outerperimeter or, in other words, the edges of the diaper 20. The periphery60 comprises the longitudinal edges 62 and the end edges 64.

While each elasticized leg cuff 32 may be configured so as to be similarto any of the leg bands, side flaps, barrier cuffs, or elastic cuffsdescribed above, it is preferred that each elasticized leg cuff 32comprise at least an inner barrier cuff 84 comprising a barrier flap 85and a spacing elastic member 86 such as described in theabove-referenced U.S. Pat. No. 4,909,803. In a preferred embodiment, theelasticized leg cuff 32 additionally comprises an elastic gasketing cuff104 with one or more elastic strands 105, positioned outboard of thebarrier cuff 84 such as described in the above-references U.S. Pat. No.4,695,278.

The diaper 20 may further comprise an elastic waist feature 34 thatprovides improved fit and containment. The elastic waist feature 34 atleast extends longitudinally outwardly from at least one of the waistedges 83 of the absorbent core 28 in at least the central region 68 andgenerally forms at least a portion of the end edge 64 of the diaper 20.Thus, the elastic waist feature 34 comprises that portion of the diaperat least extending from the waist edge 83 of the absorbent core 28 tothe end edge 64 of the diaper 20 and is intended to be placed adjacentthe wearer's waist. Disposable diapers are generally constructed so asto have two elastic waist features, one positioned in the first waistregion and one positioned in the second waist region.

The elasticized waist band 35 of the elastic waist feature 34 maycomprise a portion of the topsheet 24, a portion of the backsheet 26that has preferably been mechanically stretched and a bi-laminatematerial comprising an elastomeric member 76 positioned between thetopsheet 24 and backsheet 26 and resilient member 77 positioned betweenbacksheet 26 and elastomeric member 76.

This as well as other components of the diaper are given in more detailin WO 93/16669 which is incorporated herein by reference.

Absorbent Core

The absorbent core should be generally compressible, conformable,non-irritating to the wearer's skin, and capable of absorbing andretaining liquids such as urine and other certain body exudates. Asshown in FIG. 6, the absorbent core has a garment surface (“lower” or“bottom” part), a body surface, side edges, and waist edges. Theabsorbent core may—in addition to the fluid distribution memberaccording to the present invention—comprise a wide variety ofliquid-absorbent or liquid handling materials commonly used indisposable diapers and other absorbent articles such as—but not limitedto—comminuted wood pulp which is generally referred to as airfelt;meltblown polymers including coform; chemically stiffened, modified orcross-linked cellulosic fibers; tissue including tissue wraps and tissuelaminates.

General examples for absorbent structures are described in U.S. Pat. No.4,610,678 entitled “High-Density Absorbent Structures” issued to Weismanet al. on Sep. 9, 1986; U.S. Pat. No. 4,673,402 entitled “AbsorbentArticles With Dual-Layered Cores” issued to Weisman et al. on Jun. 16,1987; U.S. Pat. No. 4,888,231 entitled “Absorbent Core Having A DustingLayer” issued to Angstadt on Dec. 19, 1989; EP-A-0 640 330 ofBewick-Sonntag et al.; U.S. Pat. No. 5,180,622 (Berg et al.); U.S. Pat.No. 5,102,597 (Roe et al.); U.S. Pat. No. 5,387,207 (LaVon). Such andsimilar structures might be adopted to be compatible with therequirements outlined below for being used as the absorbent core 28.

The absorbent core can be a unitary core structure, or it can be acombination of several absorbent structures, which in turn can consistof one or more sub-structures. Each of the structures or sub-structurescan have an essentially two-dimensional extension (i.e. be a layer) or athree-dimensional shape.

Regions of Absorbent Articles

Generally, absorbent hygienic articles are intended for being wornaround the lower end of the body torso. It is an essential designfeature of these articles to cover the regions of the body where thedischarges occur (“discharge regions”), which extend around therespective body openings. The respective zones of the absorbent articlecovering the discharge regions are correspondingly referred to as“loading zones”. Thus during use, the articles are generally arranged onthe wearer such that they extend (for a standing position of the wearer)from the crotch between the legs upwards, both in the front and the backof the wearer.

Generally, such articles have a length dimension exceeding their widthdimension, whereby the article is worn such that the axis of the lengthdimension is aligned with the height direction of the wearer whenstanding, whilst the width direction of the article is aligned with aline extending from left to right of the wearer.

Because of the anatomy of the human wearer, the space between the legsof the wearer generally confines the space available for the article inthis region. For good fit, an absorbent article should be designed suchthat it fits well in the crotch region. If the width of the article isexcessively wide relative to the crotch width of the wearer, the articlemay be deformed, which might results in deteriorated performance, andreduced wearers comfort.

The point, where the article has its smallest width to fit best betweenthe legs of the wearer then coincides with the point on the wearer,where the distance between the legs is the narrowest, and is—for thescope of the present invention—referred to as the “crotch point”.

If the crotch point of an article is not obvious from its shape, it canbe determined by placing the article on a wearer of the intended usergroup (e.g. a toddler) preferably in a standing position, and thenplacing an extensible filament around the legs in a figure eightconfiguration. The point in the article corresponding to the point ofintersection of the filament is deemed to be the crotch point of thearticle and consequently also of the absorbent core being affixed withinthis article.

Whilst this crotch point of the article is often in the middle of thearticle (in longitudinal direction) this is not necessarily the case. Itcan very well be, that the part of the article which is intended to beworn in the front is smaller than the back (or rear) part—either in itslength dimension, or width, or both, or surface area. Also, the crotchpoint does not need to be positioned in the middle of the absorbentcore, in particular when the absorbent core is not placed longitudinallycentred within the article.

The crotch region is the area surrounding the crotch point, so as tocover the respective body openings, respectively discharge regions.Unless otherwise mentioned, this region extends over a length of 50% ofthe total core length (which, in turn is defined as the distance betweenthe front and rear waist edges of the core, which might be approximatedby straight lines perpendicular to the longitudinal center line). If thecrotch point is positioned in the middle of the article, then the crotchregion starts (when counting from the front core edge) at 25% of totallength and extends up to 75% of the total core length. Or, the front andthe rear quarter of the length of the absorbent core do not belong tothe crotch region, the rest does.

The crotch region length being 50% of the total absorbent core lengthhas been derived for baby diapers, where it has been confirmed that thisis a suitable means to describe the fluid handling phenomena. If thepresent invention is applied in articles having drastically differentdimensions, it might become necessary to reduce these 50% (as in thecase for Severe Incontinence articles) or to increase this ratio (as inthe case for Ultra Light or Light Incontinence articles). In moregeneral terms, this crotch region of the article should not extend muchbeyond the discharge region of the wearer.

If the crotch point is positioned offset from the mid-point of thearticle, the crotch region still covers 50% of the total article length(in longitudinal direction), however, not evenly distributed betweenfront and back, but proportionally adjusted to this off-set.

As an example for an article having a total core length of 500 mm, andhaving a crotch point which is positioned centered, the crotch regionwill extend from 125 mm away from the front edge up to 375 mm away fromfront edge. Or, if the crotch point lies 50 mm offset towards the frontcore edge, (i.e. being 200 mm away from front core edge), the crotchregion extends from 100 mm to 350 mm.

In general terms, for an article having a total core length of L_(c), acrotch point being at a distance L_(cp) away from the front core edge,and a crotch zone length of L_(cz), the front edge of said crotch zonewill be positioned at a distance

L _(fecz) =L _(cp)*(1−L _(cz) /L _(c)).

For example the absorbent article can be a baby diaper, for being wornby toddlers (i.e. of about 12 to 18 kg baby weight) whereby the size ofthe article in the trade is generally referred to as MAXI size. Then thearticle has to be able to receive and retain both fecal materials andurine, whereas for the context of the present invention the crotchregion has to be capable to primarily receive urine loadings.

The total area and size of the crotch region is—of course—also dependingon the respective width of the absorbent core, i.e. if the core isnarrower in the crotch region than outside the crotch region, the crotchregion has a smaller area (surface) than the remaining area of theabsorbent core.

Whilst it can be contemplated, that the boundaries between crotch regionand the rest of the article can also be curvilinear, they areapproximated within the present description to be straight lines,perpendicular to the longitudinal axis of the article.

The “crotch region” is further confined by the width of the core in thisrespective region, and the “crotch region area” by the surface as beingdefined by the crotch region length and the respective width.

As a complementary element to the crotch region, the absorbent core alsocomprises at least one but mostly two waist region(s), extending towardsthe front and/or the rear of the absorbent core outside the crotchregion.

Design Capacity and Ultimate Storage Capacity

In order to be able to compare absorbent articles for varying end useconditions, or differently sized articles, the “design capacity” hasbeen found to be a suitable measure.

For example, babies are representing a typical usage group, but evenwithin this group the amount of urine loading, frequency of loading,composition of the urine will vary widely from smaller babies (new-bornbabies) to toddlers on one side, but also for example among variousindividual babies.

Another user group may be larger children, still suffering from acertain form of incontinence.

Also, incontinent adults can use such articles, again with a wide rangeof loading conditions, generally referred to as light incontinenceranging up to severe incontinence.

Whilst the man skilled in the art will readily be able to transfer theteaching to other sizes for further discussion, focus will be put on thetoddler sized babies. For such user, urine loadings of up to 75 ml pervoiding, with on an average of four voidings per wearing periodresulting in a total loading of 300 ml, and voiding rates of 15 ml/sechave been found to be sufficiently representative.

Henceforth, such articles being able to cope with such requirementsshould have the capability of picking up such amounts of urine, whichwill be referred to for the further discussion as “design capacity”.

These amounts of fluids have to be absorbed by materials which canultimately store the bodily fluids, or at least the aqueous parts ofthese, such that—if any—only little fluid is left on the surface of thearticle towards the wearers skin. The term “ultimate” refers in onerespect to the situation as in the absorbent article at long wearingtimes, in the other respect to absorbent materials which reach their“ultimate” capacity when being equilibrated with their environment. Thiscan be in such an absorbent article under real in-use conditions afterlong wearing times, or this also can be in a test procedure for purematerials or material composites. As many of the processes underconsideration have asymptotic kinetic behavior, one skilled in the artwill readily consider “ultimate” capacities to be reached when theactual capacity has reached a value sufficiently close to the asymptoticendpoint, e.g. relative to the equipment measurement accuracy.

As an absorbent article can comprise materials which are primarilydesigned to ultimately store fluids, and other materials which areprimarily designed to fulfill other functions such as acquisition and/ordistribution of the fluid, but may still have a certain ultimate storagecapability, suitable core materials according to the present inventionare described without attempting to artificially separate suchfunctions. Nonetheless, the ultimate storage capacity can be determinedfor the total absorbent core, for regions thereof, for absorbentstructures, or even sub-structures, but also for materials as being usedin any of the previous.

As discussed in the above for varying the dimensions of the article, oneskilled in the art will be able to readily adopt the appropriate designcapacities for other intended user groups.

Materials for Being Used in Absorbent Cores

The absorbent core for the present invention can comprise fibrousmaterials to form fibrous web or fibrous matrices.

Fibers useful in the present invention include those that are naturallyoccurring fibers (modified or unmodified), as well as synthetically madefibers. Examples of suitable unmodified/modified naturally occurringfibers include cotton, Esparto grass, bagasse, kemp, flax, silk, wool,wood pulp, chemically modified wood pulp, jute, rayon, ethyl cellulose,and cellulose acetate. Suitable synthetic fibers can be made frompolyvinyl chloride, polyvinyl fluoride, polytetrafluoroethylene,polyvinylidene chloride, polyacrylics such as ORLON®, polyvinyl acetate,polyethylvinyl acetate, non-soluble or soluble polyvinyl alcohol,polyolefins such as polyethylene (e.g., PULPEX®) and polypropylene,polyamides such as nylon, polyesters such as DACRON® or KODEL®,polyurethanes, polystyrenes, and the like. The fibers used can comprisesolely naturally occurring fibers, solely synthetic fibers, or anycompatible combination of naturally occurring and synthetic fibers. Thefibers used in the present invention can be hydrophilic, or can be acombination of both hydrophilic and hydrophobic fibers.

For many absorbent cores or core structures according to the presentinvention, the use of hydrophilic fibers is preferred. Suitablehydrophilic fibers for use in the present invention include cellulosicfibers, modified cellulosic fibers, rayon, polyester fibers such aspolyethylene terephthalate (e.g., DACRON®), hydrophilic nylon(HYDROFIL®), and the like. Suitable hydrophilic fibers can also beobtained by hydrophilizing hydrophobic fibers, such assurfactant-treated or silica-treated thermoplastic fibers derived from,for example, polyolefins such as polyethylene or polypropylene,polyacrylics, polyamides, polystyrenes, polyurethanes and the like.

Suitable wood pulp fibers can be obtained from many well-known chemicalprocesses such as—but not limited to—the Kraft and sulfite processes. Afurther suitable type of fibers is chemically stiffened cellulose. Asused herein, the term “chemically stiffened cellulosic fibers” meanscellulosic fibers that have been stiffened by chemical means to increasethe stiffness of the fibers under both dry and aqueous conditions. Suchmeans can include the addition of a chemical stiffening agent that, forexample, coats and/or impregnates the fibers. Such means can alsoinclude the stiffening of the fibers by altering the chemical structure,e.g., by crosslinking polymer chains.

Polymeric stiffening agents that can coat or impregnate the cellulosicfibers include: cationic modified starches having nitrogen-containinggroups (e.g., amino groups) such as those available from National Starchand Chemical Corp., Bridgewater, N.J., USA; latexes; wet strength resinssuch as polyamide-epichlorohydrin resin (e.g., Kymene® 557H, Hercules,Inc. Wilmington, Del., USA), polyacrylamide resins described, forexample, in U.S. Pat. No. 3,556,932 (Coscia et al), issued Jan. 19,1971; commercially available polyacrylamides marketed by AmericanCyanamid Co., Stamford, Conn., USA, under the tradename Parez® 631 NC;urea formaldehyde and melamine formaldehyde resins, and polyethylenimineresins.

These fibers can also be stiffened by chemical reaction. For example,crosslinking agents can be applied to the fibers that, subsequent toapplication, are caused to chemically form intrafiber crosslink bonds.These crosslink bonds can increase the stiffness of the fibers. Whilethe utilisation of intrafiber crosslink bonds to chemically stiffen thefiber is preferred, it is not meant to exclude other types of reactionsfor chemical stiffening of the fibers.

Fibers stiffened by crosslink bonds in individualised form (i.e., theindividualised stiffened fibers, as well as process for theirpreparation) are disclosed, for example, in U.S. Pat. No. 3,224,926(Bernardin), issued Dec. 21, 1965; U.S. Pat. No. 3,440,135 (Chung),issued Apr. 22, 1969; U.S. Pat. No. 3,932,209 (Chatterjee), issued Jan.13, 1976; and U.S. Pat. No. 4,035,147 (Sangenis et al), issued Dec. 19,1989; U.S. Pat. No. 4,898,642d (Moore et al), issued Feb. 6, 1990; andU.S. Pat. No. 5,137,537 (Herron et al), issued Aug. 11, 1992.

In currently preferred stiffened fibers, chemical processing includesintrafiber crosslinking with crosslinking agents while such fibers arein a relatively dehydrated, defibrated (i.e., individualised), twisted,curled condition. Suitable chemical stiffening agents are typicallymonomeric crosslinking agents including, especially C₂-C₉ polycarboxylicacids such as citric acid. Preferably, such stiffened fibers are twistedand curledas descibed in more details in U.S. Pat. No. 4,898,642.

These chemically stiffened cellulosic fibers have certain propertiesthat make them particularly useful in certain absorbent structuresaccording to the present invention, relative to unstiffened cellulosicfibers. In addition to being hydrophilic, these stiffened fibers haveunique combinations of stiffness and resiliency.

In addition to or alternatively synthetic or thermoplastic fibers cancomprised in the absorbent structures, such as being made from anythermoplastic polymer that can be melted at temperatures that will notextensively damage the fibers. Preferably, the melting point of thisthermoplastic material will be less than about 190° C., and preferablybetween about 75° C. and about 175° C. In any event, the melting pointof this thermoplastic material should be no lower than the temperatureat which the thermally bonded absorbent structures, when used inabsorbent articles, are likely to be stored. The melting point of thethermoplastic material is typically no lower than about 50° C.

The thermoplastic materials, and in particular the thermoplastic fibers,can be made from a variety of thermoplastic polymers, includingpolyolefins such as polyethylene (e.g., PULPEX®) and polypropylene,polyesters, copolyesters, polyvinyl acetate, polyamides, copolyamides,polystyrenes, polyurethanes and copolymers of any of the foregoing suchas vinyl chloride/vinyl acetate, and the like. Suitable thermoplasticmaterials include hydrophobic fibers that have been made hydrophilic,such as surfactant-treated or silica-treated thermoplastic fibersderived from, for example, polyolefins such as polyethylene orpolypropylene, polyacrylics, polyamides, polystyrenes, polyurethanes andthe like. The surface of the hydrophobic thermoplastic fiber can berendered hydrophilic by treatment with a surfactant, such as a nonionicor anionic surfactant, e.g., by spraying the fiber with a surfactant, bydipping the fiber into a surfactant or by including the surfactant aspart of the polymer melt in producing the thermoplastic fiber. Uponmelting and resolidification, the surfactant will tend to remain at thesurfaces of the thermoplastic fiber. Suitable surfactants includenonionic surfactants such as Brij® 76 manufactured by ICI Americas, Inc.of Wilmington, Del., and various surfactants sold under Pegosperse®trademark by Glyco Chemical, Inc. of Greenwich, Conn. Besides nonionicsurfactants, anionic surfactants can also be used. These surfactants canbe applied to the thermoplastic fibers at levels of, for example, fromabout 0.2 to about 1 gram per square of centimetre of thermoplasticfiber.

Suitable thermoplastic fibers can be made from a single polymer(monocomponent fibers), or can be made from more than one polymer (e.g.,bicomponent fibers). For example, “bicomponent fibers” can refer tothermoplastic fibers that comprise a core fiber made from one polymerthat is encased within a thermoplastic sheath made from a differentpolymer. The polymer comprising the sheath often melts at a different,typically lower, temperature than the polymer comprising the core. As aresult, these bicomponent fibers provide thermal bonding due to meltingof the sheath polymer, while retaining the desirable strengthcharacteristics of the core polymer.

Suitable bicomponent fibers for use in the present invention can includesheath/core fibers having the following polymer combinations:polyethylene/polypropylene, polyethylvinyl acetate/polypropylene,polyethylene/polyester, polypropylene/polyester, copolyester/polyester,and the like. Particularly suitable bicomponent thermoplastic fibers foruse herein are those having a polypropylene or polyester core, and alower melting copolyester, polyethylvinyl acetate or polyethylene sheath(e.g., DANAKLON®, CELBOND®) or CHISSO® bicomponent fibers). Thesebicomponent fibers can be concentric or eccentric. As used herein, theterms “concentric” and “eccentric” refer to whether the sheath has athickness that is even, or uneven, through the cross-sectional area ofthe bicomponent fiber. Eccentric bicomponent fibers can be desirable inproviding more compressive strength at lower fiber thicknesses. Suitablebicomponent fibers for use herein can be either uncrimped (i.e. bent).Bicomponent fibers can be crimped by typical textile means such as, forexample, a stuffer boy method or the gear crimp method to achieve apredominantly two-dimensional or “flat” crimp.

In the case of thermoplastic fibers, their length can vary dependingupon the particular melt point and other properties desired for thesefibers. Typically, these thermoplastic fibers have a length from about0.3 to about 7.5 cm long, preferably from about 0.4 to about 3.0 cmlong. The properties, including melt point, of these thermoplasticfibers can also be adjusted by varying the diameter (caliper) of thefibers. The diameter of these thermoplastic fibers is typically definedin terms of either denier (grams per 9000 meters) or decitex (grams per10,000 meters dtex). Depending on the specific arrangement within thestructure, suitable thermoplastic fibers can have a decitex in the rangefrom well below 1 decitex, such as 0.4 decitex to about 20 dtex.

Said fibrous materials may be used in an individualised form when theabsorbent article is being produced, and an airlaid fibrous structure isformed on the line. Said fibers may also be used as a preformed fibrousweb or tissue. These structures are then delivered to the production ofthe article essentially in endless or very long form (e.g. on a roll,spool) and will then be cut to the appropriate size. This can be done oneach of such materials individually before these are combined with othermaterials to form the absorbent core, of when the core itself is cut andsaid materials are co-extensive with the core.

There is a wide variety of making such web, and such processes are verywell known in the art.

With regard to fibers used for producing such webs, there is nearly nolimitation in principle—though certain specific web forming and bondingprocesses might not be fully compatible with certain materials or fibertypes.

When looking at individualised fibers as a starting material for makinga web, these can be laid down in a fluid medium—if this is gaseous (air)such structures are generally referred to as “dry-laid”, if it is liquidsuch structures are generally referred to as “wet-laid”. “Wet-laying” isbroadly used to produce paper tissues with a wide range of properties.This term is most commonly used with cellulosic materials, however, alsosynthetic fibers can be included.

“Dry-laying” is broadly used for non-woven webs, and often the cardingprocess can be used to form such webs. Also the commonly known “air-laidtissues” fall under this category.

A molten polymer can be extruded into fibers which then can be formeddirectly into a web (i.e. omitting the process step of making individualfibers which then are formed into a web in a separate process step). Theresulting structures are commonly referred to as non-wovens of themeltblown type or—if fibers are significantly more drawn—spunbondedwebs.

Further, webs can also be formed by combining one or more of the otherformation technologies.

In order to give certain strength and integrity properties to the webstructures, these are generally bonded. The most broadly usedtechnologies are (a) chemical bonding or (b) thermo bonding by melting apart of the web such. For the latter, the fibers can be compressed,resulting in distinct bonding points, which, for example for nonwovenmaterials, can cover a significant portion of the total area, values of20% are not uncommon. Or—particularly useful for structures where lowdensities are desired—“air-through” bonding can be applied, where partsof the polymers e.g. the sheath material of a BiCo-fibers are molten bymeans of heated air passing through the (often air-laid) web.

After the webs are formed and bonded, these can be further treated tomodify specific properties. This can be—as one of many possibleexamples—additional surfactant to render hydrophobic fibers morehydrophilic, or vice versa. Also, post formation mechanical treatment,such as disclosed in EP application 96108427.4 can be used to impartparticularly useful properties to such materials.

In addition or alternatively to fibrous webs, the absorbent cores maycomprise other porous materials, such as foams. Preferred foams areopen-celled absorbent polymeric foam materials as being derived bypolymerising a High Internal Phase Water-in-Oil Emulsion (hereafterreferred to a HIPE). Such polymeric foams may be formed to provide therequisite storage properties, as well as the requisite distributionproperties.

HIPE-derived foams which provide both the requisite distribution andstorage properties for use herein are described in copending U.S. patentapplication Ser. No. 08/563,866 (DesMarais et al.), filed Nov. 25, 1995(hereafter referred to as “'866 application”), the disclosure of whichis hereby incorporated by reference; copending U.S. patent applicationSer. No. 08/542,497, filed Oct. 13, 1995 (Dyer et al.); U.S. Pat. No.5,387,207 (Dyer et al.), issued Feb. 7, 1995; and U.S. Pat. No.5,260,345 (DesMarais et al.), issued Nov. 9, 1993; the disclosure ofeach of which is hereby incorporated by reference.

Polymeric foams useful in the present invention are those which arerelatively open-celled. This means the individual cells of the foam arein complete, unobstructed communication with adjoining cells. The cellsin such substantially open-celled foam structures have intercellularopenings or “windows” that are large enough to permit ready fluidtransfer from one cell to the other within the foam structure.

These substantially open-celled foam structures will generally have areticulated character with the individual cells being defined by aplurality of mutually connected, three dimensionally branched webs. Thestrands of polymeric material making up these branched webs can bereferred to as “struts.” As used herein, a foam material is“open-celled” if at least 80% of the cells in the foam structure thatare at least 1 micro meter in size are in fluid communication with atleast one adjacent cell.

In addition to being open-celled, these polymeric foams are sufficientlyhydrophilic to permit the foam to absorb aqueous fluids in the amountsspecified hereafter. The internal surfaces of the foam structures arerendered hydrophilic by residual hydrophilizing surfactants left in thefoam structure after polymerization, or by selected post-polymerizationfoam treatment procedures.

The polymeric foams can be prepared in the form of collapsed (i.e.unexpanded), polymeric foams that, upon contact with aqueous fluids,expand and absorb such fluids. See, for example, copending U.S. patentapplication Ser. No. 08/563,866 and U.S. Pat. No. 5,387,207. Thesecollapsed polymeric foams are usually obtained by expressing the waterphase from the polymerized HIPE foam through compressive forces, and/orthermal drying and/or vacuum dewatering. After compression, and/orthermal drying/vacuum dewatering, the polymeric foam is in a collapsed,or unexpanded state. Alternatively, such foams can be non-collapsiblefoams, such as those described copending U.S. patent application Ser.No. 081542,497 and U.S. Pat. No. 5,260,345.

Superabsorbent Polymers or Hydrogels

Optionally, and often preferably, the absorbent structures according tothe present invention can comprise superabsorbent polymers, orhydrogels. The hydrogel-forming absorbent polymers useful in the presentinvention include a variety of substantially water-insoluble, butwater-swellable polymers capable of absorbing large quantities ofliquids. Such polymer materials are also commonly referred to as“hydrocolloids”, or “superabsorbent” materials. These hydrogel-formingabsorbent polymers preferably have a multiplicity of anionic, functionalgroups, such as sulfonic acid, and more typically carboxy, groups.Examples of polymers suitable for use herein include those which areprepared from polymerisable, unsaturated, acid-containing monomers.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the hydrogel-forming absorbent polymers herein. Suchnon-acid monomers can include, for example, the water-soluble orwater-dispersible esters of the acid-containing monomers, as well asmonomers that contain no carboxylic or sulfonic acid groups at all.Examples for such well known materials are described e.g. in U.S. Pat.No. 4,076,663 (Masuda et al), issued Feb. 28, 1978, and in U.S. Pat. No.4,062,817 (Westerman), issued Dec. 13, 1977.

Hydrogel-forming absorbent polymers suitable for the present inventioncontain carboxy groups. These polymers include hydrolysedstarch-acrylonitrile graft copolymers, partially neutralisedstarch-acrylonitrile graft copolymers, starch-acrylic acid graftcopolymers, partially neutralised starch-acrylic acid graft copolymers,saponified vinyl acetate-acrylic ester copolymers, hydrolysedacrylonitrile or acrylamide copolymers, slightly network crosslinkedpolymers of any of the foregoing copolymers, partially neutralisedpolyacrylic acid, and slightly network crosslinked polymers of partiallyneutralised polyacrylic acid. These polymers can be used either solelyor in the form of a mixture of two or more different polymers. Examplesof these polymer materials are disclosed in U.S. Pat. Nos. 3,661,875,4,076,663, 4,093,776, 4,666,983, and 4,734,478.

Most preferred polymer materials for use in making hydrogel-formingparticles are slightly network crosslinked polymers of partiallyneutralised polyacrylic acids and starch derivatives thereof. Mostpreferably, the hydrogel-forming particles comprise from about 50 toabout 95%, preferably about 75%, neutralised, slightly networkcrosslinked, polyacrylic acid (i.e. poly (sodium acrylate/acrylicacid)).

As described above, the hydrogel-forming absorbent polymers arepreferably slightly network crosslinked. Network crosslinking serves torender the polymer substantially water-insoluble and, in part,determines the absorptive capacity and extractable polymer contentcharacteristics of the precursor particles and the resultantmacrostructures. Processes for network crosslinking the polymers andtypical network crosslinking agents are described in greater detail inthe herein before-referenced U.S. Pat. No. 4,076,663, and inDE-A-4020780 (Dahmen).

The superabsorbent materials can be used in particulate form or infibrous form and may also be combined other elements to form preformedstructures.

Whilst the individual elements have been disclosed separately, andabsorbent structure or substructure can be made by combining one or moreof these elements.

Without intending a limiting effect, the following describes suitablecombinations.

i) Particular Superabsorbent polymer (SAP) mixed with cellulosic orother fibers. The basic principle is well established and known,however, upon attempting to reduce thinness of the articles, higher andhigher ratios of weight of SAP to fibers have been employed recently.Within this scope, combination of the SAP with binders such as hot-meltadhesives (such as disclosed in EP-A-0,695,541) or with meltablepolymeric material (such as PE particles) can be a suitable tool toimmobilise the SAP;

ii) SAP forming a substructure by interparticle crosslinks;

iii) Fibrous SAP being mixed with other fibers, or forming a fibrous SAPweb;

iv) foam structures comprising differing in pore sizes etc.

Improved Absorbent Articles

After having described absorbent articles and suitable members,materials, structures, components or sub-components in general terms,the following will describe the requirements for the fluid storage andfluid distribution members according to the present invention, as wellas the materials suitable for being used in such members.

Improved Distribution Member

The requirements for the distribution members can be determined byeither looking at the member or at the materials contained in saidmember. Henceforth, the requirements as laid out in the presentdescription have to be satisfied for either the total member or for therespective materials therein.

Henceforth, distribution members or materials useful for such membersaccording to the present invention can be described by the followingimportant parameter:

First, the permeability at full saturation (k100) of the member ormaterial. Conventional distribution materials have this permeabilitybalanced so as to find the optimum between having little resistance tothe fluid flow (i.e. high permeability) and sufficient capillarypressure so as to provide wicking properties, such as results fromsmaller pore sizes (i.e. lower permeability). The permeability at fullsaturation (k100) should generally be more than 1 Darcy (with 1 Darcycorresponding to 9.869* 10⁻¹³ m²), preferably more than 2 Darcy, or even8 Darcy, or even more preferably more than 100 Darcy. The fullsaturation can be determined by the Capsorption test as describedhereinafter as the maximum uptake, corresponding to the result CapillarySorption Absorption Capacity at 0 cm height (CSAC 0).

Second, the dependency of the permeability on the degree of saturation.This property has not been considered in previous material designconsiderations, and conventional materials have a stronglysub-proportional behavior, i.e. the actual permeability at a degree ofsaturation of less than 100% is significantly lower than it would be fora linear correlation between actual permeability and saturation.

Thirdly, the Capillary Sorption Pressure, namely the Capillary SorptionDesorption pressure, such as measured in the Capillary Sorption Test asdescribed hereinafter. This parameter describes the ability of thematerials or members to release liquids, to satisfy their role as adistribution element in an absorbent article.

Additionally and often preferably, the distribution materials maysatisfy the requirement of high fluid flux rates in the vertical wickingflux test as described herein after. Preferably, the materials provideat a wicking height of 15 cm a flux of at least 0.045 g/cm²/sec,preferably more than 0.06 g/cm²/sec, and even more preferably more than0.10 g/cm²/sec.

With careful selection of materials satisfying the right balance of thethese parameter, important benefits can be realized for the absorbentstructures and/or respective articles.

First, the liquid distribution materials are readily dewatered afterthey have been loaded such as with a urine gush. This is relevant so asto allow these materials to be ready for receiving a subsequent loadingas it often occurs in real use.

Second, these materials allow a more even liquid distribution ofliquids, even at loads which are relatively small compared to the designcapacity. This is even more important for designs which aim atmaintaining an improved fit on the wearer by avoiding high liquidaccumulation in certain regions of the article, but rather aim for aneven distribution of the liquid stored.

Thirdly, if the materials also satisfy the high flux requirements, theliquid can be well and quickly distributed even against gravity. Thisbecomes particularly relevant, if the ultimate storage of the fluid isintended to be distant to the loading zone or area. These materials aretherefore especially useful in core designs such as described in PCTApplication U.S. Ser. No. 97/05046 filed on Mar. 27, 1997.

The permeability of the materials or members are determined by thepermeability tests as described hereinafter.

Without wishing to be bound by the theory, it is believed, that theactual permeability k{S} has a dependency from the degree of saturation,which for many relevant systems can be approximated by the followingequation (see also “Dynamics of fluids in porous media” by J. Bear,Haifa, publ. Dover Publications, Inc., New York, 1988, esp. pages 461ff,491ff):

k{S}=k{100}*{S ^(SDP)}

wherein k denotes the permeability in units of Darcy; and SDP representsthe dimensionless exponent or Saturation Dependency Parameter describingthe sub-proportional behavior. S denotes the degree of saturation,ranging from 0 to 1, wherein the value of 1 corresponds to fullsaturation (i.e. 100% saturation) under zero external and/or capillarypressure).

Conventional design criteria for distribution materials focused on highvalues for permeability at saturation (k100), which of course could leadto structures having little or no wicking capability, thus beingsuitable as acquisition material, wherein essentially the “free flowregime” should be controlled, but not for distribution materials. Suchmaterials would have very poor transport properties under wickingconditions, such as transporting against gravity. Such extremeproperties are found in conventional acquisition materials, thoughdistribution material such as described in European Patent ApplicationEP-A-0,809,991 provide a combination of a wicking ability and free flowcontrol—but still under full saturation conditions.

Materials according to the present invention exhibit a permeabilityk(100) of at least 1 Darcy, preferably at least 2 Darcy. Higher valuesfor the permeability provide an even less reduced resistance to thefluid transport, and are preferred as long as this is achieved withoutviolating the further requirements as laid out herein. In particular,materials having a permeability of more than 8 Darcy or even more than100 Darcy can be very suitable.

As can be seen from the equation, a higher value for the SDP parameterdescribes systems with a stronger sub-proportional behavior—if the SDPwere equal to one, a linear relation would exist. Conventionaldistribution materials exhibit a strong sub-proportional behavior, suchas can be described by SDP having values of 3 or more. For such a value,the permeability at 50% saturation is only 12.5% of the permeability at100% saturation, thus also the ability for receiving and distributingfurther liquid load is dramatically reduced.

Henceforth, materials according to the present invention have a SDPvalue of less than 3, preferably less than 2.75, even more preferablyless than 2.5, and values of less than 2 are even better. Such valuescorrespond to a permeability at 50% saturation of more than 14% of thepermeability at 100% saturation, preferably more than about 18%, evenmore preferably more than about 25% and values of more than 35% are evenbetter. Such values correspond to a permeability at 30% saturation ofmore than about 3.5% of the permeability at 100% saturation, preferablymore than about 5%, even more preferably more than about 10%.

The simplified permeability test as laid out hereinafter can measure the“trans-planar” permeability, i.e. the permeability in the thicknessdimension of the sample as determined, and—with a modified samplecell—also the “in-plane” permeability. For a number of materials, suchas isotropically foamed foams, the trans-planar and the in-planepermeability will be essentially identical. This Simplified PermeabilityTest provides a simple test set up to measure permeability for twospecial conditions: Either the permeability can be measured for a widerange of porous materials (such as non-wovens made of synthetic fibres,or cellulosic structures) at 100% saturation, or for materials, whichreach different degrees of saturation with a proportional change incaliper without being filled with air (respectively the outside vapourphase) for which the permeability at varying degrees of saturation canreadily be measured at various thicknesses.

For example the described collapsible foams exhibit a thickness orcaliper, which is dependent on the degree of fluid load or saturation,i.e. they have a certain thickness at saturation, which is being reducedupon removal of fluid, as the foam pores are of such a size, that theycollapse upon removal of liquid from them. Conversely, a certain calipercan be set to define a certain degree of loading. Thus, such materialsthe Simplified Permeability Test can be readily applied to determine thedependency of the permeability on the saturation.

The General Permeability Test as described hereinafter is useful fordetermining the dependency of the permeability on the saturation forporous materials in the general sense, such as fibrous webs orstructures, or foams which maintain their pore size essentiallyindependent of the degree of wetting.

A further important requirement for the materials or members accordingto the present invention is their ability to release the fluid to astorage medium. This reflects the fact, that the distribution materialsor members should not retain the liquid for too long times, but only forthe time that is required to transport he fluid to the appropriatestorage material of member.

A suitable parameter to describe this property is the Capillary SorptionDesorption pressure, as determined via the member's ability to receiveand to release fluid at varying capillary pressures, herein determinedin units of water column height (“capillary height”), which aregenerally encountered when the member is positioned in an absorbentarticle. The Capillary Sorption Absorbent Capacity test (also referredto herein as the Capsorption test) measures the amount of test fluid pergram of an absorbent member or material that is taken up or releasedwhen the material or member is placed at varying heights on a capillarysorption apparatus. The Capillary Sorption Absorbent Capacity test isdescribed in greater detail in the Test Methods section below, yieldingthe Capillary Sorption Desorption Height at which the material hasreleased 50% of the amount of fluid at 0 cm sorption height (CSDH 50).

Materials useful in the context of the present invention should have aCSDH 50 of less than 150 cm, preferably less than 100 cm, even morepreferably less than 75 cm or even less than 50 cm.

Materials particularly useful for being used for the present inventionare hydrophilic, flexible polymeric foam structures of interconnectedopen-cells.

For such foams, the mechanical strength of the foam can be such that,upon giving up its liquid, the foam collapses under the capillarypressures involved. The collapse process reduces the effective foamcapacity by a substantial factor related to the density of the foam, asis described hereinafter. The collapse, if relatively uniform throughoutthe structure, also reduces the amount of liquid held in place at thepoint of liquid insult. In this regard, the strength of the foams isless than the capillary pressure exerted by the foams such that thefoams will collapse when the aqueous liquids are removed by the storagecomponent of the core. Capillary pressure is controlled herein primarilyby adjusting foam cell size (which relates inversely to surface area perunit volume). Strength is controlled by the combination of crosslinkdensity and foam density, which can be expressed as crosslink densityper unit volume as defined hereinafter. The type of crosslinker andother comonomers can also be influential.

Polymeric foams useful herein are those which are relativelyopen-celled. The cells in such substantially open-celled foam structureshave intercellular openings or “windows” that are large enough to permitready liquid transfer from one cell to the other within the foamstructure.

These substantially open-celled foam structures will generally have areticulated character with the individual cells being defined by aplurality of mutually connected, three dimensionally branched webs. Thestrands of polymeric material making up these branched webs can bereferred to as “struts.” For purposes of the present invention, a foammaterial is “open-celled” if at least 80% of the cells in the foamstructure that are at least 1 μm in size are in fluid communication withat least one adjacent cell.

In addition to being open-celled, these polymeric foams are sufficientlyhydrophilic to permit the foam to absorb aqueous liquids. The internalsurfaces of the foam structures are rendered hydrophilic by residualhydrophilizing surfactants and/or salts left in the foam structure afterpolymerization, or by selected post-polymerization foam treatmentprocedures, as described hereafter.

The extent to which these polymeric foams are “hydrophilic” can bequantified by the “adhesion tension” value exhibited when in contactwith an absorbable test liquid. The adhesion tension exhibited by thesefoams can be determined experimentally using a procedure where weightuptake of a test liquid, e.g., synthetic urine, is measured for a sampleof known dimensions and capillary suction specific surface area. Such aprocedure is described in greater detail in the Test Methods section ofU.S. Pat. No. 5,387,207 (Dyer et al.) issued Feb. 7, 1995, which isincorporated by reference. Foams which are useful as distributionmaterials of the present invention are generally those which exhibit anadhesion tension value of from about 15 to about 65 dynes/cm, morepreferably from about 20 to about 65 dynes/cm, as determined bycapillary suction uptake of synthetic urine having a surface tension of65±5 dynes/cm.

An important aspect of these foams is their glass transition temperature(Tg). The Tg represents the midpoint of the transition between theglassy and rubbery states of the polymer. Foams that have a higher Tgthan the temperature of use can be very strong but can also be veryrigid and potentially prone to fracture. Such foams also tend to creepunder stress and be poorly resilient when used at temperatures colderthan the Tg of the polymer. The desired combination of mechanicalproperties, specifically strength and resilience, typically necessitatesa fairly selective range of monomer types and levels to achieve thesedesired properties.

For distribution foams useful for the present invention, the Tg shouldbe as low as possible, so long as the foam has acceptable strength.Accordingly, monomers are selected as much as possible that providecorresponding homopolymers having lower Tg's.

The shape of the glass transition region of the polymer can also beimportant, i.e., whether it is narrow or broad as a function oftemperature. This glass transition region shape is particularly relevantwhere the in-use temperature (usually ambient or body temperature) ofthe polymer is at or near the Tg. For example, a broader transitionregion can mean transition is incomplete at in-use temperatures.Typically, if the transition is incomplete at the in-use temperature,the polymer will evidence greater rigidity and will be less resilient.Conversely, if the transition is completed at the in-use temperature,then the polymer will exhibit faster recovery from compression.Accordingly, it is desirable to control the Tg and the breadth of thetransition region of the polymer to achieve the desired mechanicalproperties. Generally, it is preferred that the Tg of the polymer be atleast about 10° C. lower than the in-use temperature. (The Tg and thewidth of the transition region are derived from the loss tangent vs.temperature curve from a dynamic mechanical analysis (DMA) measurement,as described in U.S. Pat. No. 5,563,179 (Stone et al.) issued Oct. 8,1996.)

Polymeric foams useful for the present invention can be described by anumber of parameter.

Foams useful for the present invention are able to wick aqueous liquidsto a significant height against the force of gravity, e.g., at leastabout 15 cm. The column of liquid held within the foam exerts asignificant contractile capillary pressure. At a height determined byboth the strength of the foam (in compression) and the surface area perunit volume of the foam, the foam will collapse. This heigh is theCapillary Collapse Pressure (CCP) expressed in cm at which 50% of thevolume of the foam at zero head pressure is lost. Preferred distributionfoams useful for the present invention will have a CCP of at least about15 cm, more preferably at least about 20 cm, still more preferably atleast about 25 cm. Typically, preferred distribution foams will have acapillary collapse pressure of from about 15 cm to about 50 cm, morepreferably from about 20 cm to about 45 cm, still more preferably fromabout 25 to about 40 cm.

A feature that can be useful in defining preferred polymeric foams isthe cell structure. Foam cells, and especially cells that are formed bypolymerizing a monomer-containing oil phase that surrounds relativelymonomer-free water-phase droplets, will frequently be substantiallyspherical in shape. These spherical cells are connected to each other byopenings, which are referred to hereafter as holes between cells. Boththe size or “diameter” of such spherical cells and the diameter of theopenings (holes) between the cells are commonly used for characterizingfoams in general. Since the cells, and holes between the cells, in agiven sample of polymeric foam will not necessarily be of approximatelythe same size; average cell and hole sizes, i.e., average cell and holediameters, will often be specified.

Cell and hole sizes are parameters that can impact a number of importantmechanical and performance features of the, including the liquid wickingproperties of these foams, as well as the capillary pressure that isdeveloped within the foam structure. A number of techniques areavailable for determining the average cell and hole sizes of foams. Auseful technique involves a simple measurement based on the scanningelectron photomicrograph of a foam sample. The foams useful asabsorbents for aqueous liquids in accordance with the present inventionwill preferably have a number average cell size of from about 20 μm toabout 60 μm, and typically from about 30 μm to about 50 μm, and a numberaverage hole size of from about 5 μm to about 15 μm, and typically fromabout 8 μm to about 12 μm.

“Capillary suction specific surface area” is a measure of thetest-liquid-accessible surface area of the polymeric network accessibleto the test liquid. Capillary suction specific surface area isdetermined both by the dimensions of the cellular units in the foam andby the density of the polymer, and is thus a way of quantifying thetotal amount of solid surface provided by the foam network to the extentthat such a surface participates in absorbency.

For purposes of this invention, capillary suction specific surface areais determined by measuring the amount of capillary uptake of a lowsurface tension liquid (e.g., ethanol) which occurs within a foam sampleof a known mass and dimensions. A detailed description of such aprocedure for determining foam specific surface area via the capillarysuction method is set forth in the Test Methods section of U.S. Pat. No.5,387,207 supra. Any reasonable alternative method for determiningcapillary suction specific surface area can also be utilized.

Distribution foams useful for the present invention will preferably havea capillary suction specific surface area of at least about 0.01 m²/ml,more preferably at least about 0.03 m²/ml. Typically, the capillarysuction specific surface area is in the range from about 0.01 to about0.20 m²/ml, preferably from about 0.03 to about 0.10 m²/ml, mostpreferably from about 0.04 to about 0.08 m²/ml.

“Foam density” (i.e., in grams of foam per cubic centimeter of foamvolume in air) is specified herein on a dry basis. The density of thefoam, like capillary suction specific surface area, can influence anumber of performance and mechanical characteristics of absorbent foams.These include the absorbent capacity for aqueous liquids and thecompression deflection characteristics. Foam density will vary accordingto the state of the foam. Foams in the collapsed state obviously havehigher density than the same foam in the fully expanded state. Ingeneral, foams in the collapsed state useful for the present inventionhave a dry density of about 0.11 g/cm³.

Any suitable gravimetric procedure that will provide a determination ofmass of solid foam material per unit volume of foam structure can beused to measure foam density. For example, an ASTM gravimetric proceduredescribed more fully in the Test Methods section of U.S. Pat. No.5,387,207 supra is one method that can be employed for densitydetermination. Foam density pertains to the weight per unit volume of awashed foam free of emulsifiers, fillers, surface treatments such assalts, and the like. The foams useful for the present invention willpreferably have dry densities of from about 8 mg/cm³ to about 77 mg/cm³,more preferably from about 11 mg/cm³ to about 63 mg/cm³ still morepreferably from about 13 mg/cm³ to about 48 mg/cm³.

Foams useful for the present invention can be obtained by polymerizing aspecific type of water-in-oil emulsion or HIPE having a relatively smallamount of an oil phase and a relatively greater amount of a water phase.This process comprises the steps of:

A) forming a water-in-oil emulsion at a specified temperature and underspecified shear mixing from:

1) an oil phase comprising:

a) from about 85 to about 98% by weight of a monomer component capableof forming a copolymer having a Tg of about 35° C. or lower, the monomercomponent comprising:

i) from about 30 to about 80% by weight of at least one substantiallywater-insoluble monofunctional monomer capable of forming an atacticamorphous polymer having a Tg of about 25° C. or lower;

ii) from about 5 to about 40% by weight of at least one substantiallywater-insoluble monofunctional comonomer capable of imparting toughnessabout equivalent to that provided by styrene;

iii) from about 5 to about 30% by weight of a first substantiallywater-insoluble, polyfunctional crosslinking agent selected from divinylbenzenes, trivinylbenzenes, divinyltoluenes, divinylxylenes,divinyinaphthalenes divinylalkylbenzenes, divinylphenanthrenes,divinylbiphenyls, divinyldiphenyl-methanes, divinylbenzyls,divinylphenylethers, divinyldiphenylsulfides, divinylfurans,divinylsulfide, divinyl sulfone, and mixtures thereof; and

iv) from 0 to about 15% by weight of a second substantiallywater-insoluble, polyfunctional crosslinking agent selected frompolyfunctional acrylates, methacrylates, acrylamides, methacryl-amides,and mixtures thereof; and

b) from about 2 to about 15% by weight of an emulsifier component whichis soluble in the oil phase and which is suitable for forming a stablewater-in-oil emulsion, the emulsion component comprising: (i) a primaryemulsifier having at least about 40% by weight emulsifying componentsselected from diglycerol monoesters of linear unsaturated C₁₆-C₂₂ fattyacids, diglycerol monoesters of branched C₁₆-C₂₄ fatty acids, diglycerolmonoaliphatic ethers of branched C₁₆-C₂₄ alcohols, diglycerolmonoaliphatic ethers of linear unsaturated C₁₆-C₂₂ fatty alcohols,diglycerol monoaliphatic ethers of linear saturated C₁₂-C₁₄ alcohols,sorbitan monoesters of linear unsaturated C₁₆-C₂₂ fatty acids, sorbitanmonoesters of branched C₁₆-C₂₄ fatty acids, and mixtures thereof; or(ii) the combination a primary emulsifier having at least 20% by weightof these emulsifying components and certain secondary emulsifiers in aweight ratio of primary to secondary emulsifier of from about 50:1 toabout 1:4; and

2) a water phase comprising an aqueous solution containing: (i) fromabout 0.2 to about 20% by weight of a water-soluble electrolyte; and(ii) an effective amount of a polymerization initiator;

3) a volume to weight ratio of water phase to oil phase in the range offrom about 12:1 to about 125:1; and

B) polymerizing the monomer component in the oil phase of thewater-in-oil emulsion to form a polymeric foam material; and

C) optionally dewatering the polymeric foam material.

The process allows the formation of these absorbent foams that arecapable of distributing liquids as a result of having carefully balancedproperties as described herein. These properties are achieved by carefulselection of crosslinker and monomer types and levels and emulsionformation parameters, specifically the amount of shear mixing, thetemperature, and the water-to-oil ratio (which translates into the finaldensity of the dry foam).

Polymeric foams useful for the present invention can be prepared bypolymerization of certain water-in-oil emulsions having a relativelyhigh ratio of water phase to oil phase commonly known in the art as“HIPEs”. Polymeric foam materials which result from the polymerizationof such emulsions are referred to hereafter as “HIPE foams”. A detaileddescription of the general preparation of such HIPEs is given in U.S.Pat. Nos. 5,563,179 and 5,387,207, infra.

The relative amounts of the water and oil phases used to form the HIPEsare, among many other parameters, important in determining thestructural, mechanical and performance properties of the resultingpolymeric foams. In particular, the ratio of water to oil (“W:O ratio”)in the emulsion varies inversely with ultimate foam density and caninfluence the cell size and capillary suction specific surface area ofthe foam and dimensions of the struts that form the foam. The emulsionsused to prepare the HIPE foams useful for this invention will generallyhave a volume to weight ratio of water phase to oil phase in the rangeof from about 12:1 to about 125:1, and most typically from about 15:1 toabout 90:1. Particularly preferred foams can be made from HIPEs havingratios of from about 20:1 to about 75:1.

The major portion of the oil phase of the HIPEs will comprise monomers,comonomers and crosslinking agents such as those enumerated in U.S. Pat.No. 5,387,207 infra. It is essential that these monomers, comonomers andcrosslinking agents be substantially water-insoluble so that they areprimarily soluble in the oil phase and not the water phase. Use of suchsubstantially water-insoluble monomers ensures that HIPEs of appropriatecharacteristics and stability will be realized. It is, of course, highlypreferred that the monomers, comonomers and crosslinking agents usedherein be of the type such that the resulting polymeric foam is suitablynon-toxic and appropriately chemically stable. These monomers,comonomers and cross-linking agents should preferably have little or notoxicity if present at very low residual concentrations duringpost-polymerization foam processing and/or use.

Another essential component of the oil phase is an emulsifier componentthat permits the formation of stable HIPEs. This emulsifier componentcomprises a primary emulsifier and optionally a secondary emulsifier,such as those enumerated in U.S. Pat. No. 5,387,207 infra.

The oil phase used to form the HIPEs comprises from about 85 to about98% by weight monomer component and from about 2 to about 15% by weightemulsifier component. Preferably, the oil phase will comprise from about90 to about 98% by weight monomer component and from about 3 to about10% by weight emulsifier component. The oil phase also can contain otheroptional components. One such optional component is an oil solublepolymerization initiator of the general type well known to those skilledin the art, such as described in U.S. Pat. No. 5,290,820 (Bass et al.),issued Mar. 1, 1994, which is incorporated by reference. Anotherpreferred optional component is an antioxidant such as a Hindered AmineLight Stabilizer (HALS) and Hindered Phenolic Stabilizers (HPS) or anyother antioxidant compatible with the initiator system to be employed.Other optional components include plasticizers, fillers, colorants,chain transfer agents, dissolved polymers, and the like.

The discontinuous water internal phase of the HIPE is generally anaqueous solution containing one or more dissolved components such asthose enumerated in U.S. Pat. No. 5,387,207 infra. One essentialdissolved component of the water phase is a water-soluble electrolyte.The dissolved electrolyte minimizes the tendency of the monomers,comonomers and crosslinkers that are primarily oil soluble to alsodissolve in the water phase.

This, in turn, is believed to minimize the extent to which polymericmaterial fills the cell windows at the oil/water interfaces formed bythe water phase droplets during polymerization. Thus, the presence ofelectrolyte and the resulting ionic strength of the water phase isbelieved to determine whether and to what degree the resulting preferredpolymeric foams can be open-celled.

The HIPEs will also typically contain a polymerization initiator. Suchan initiator component is generally added to the water phase of theHIPEs and can be any conventional water-soluble free radical initiator.These include peroxygen compounds such as sodium, potassium and ammoniumpersulfates, hydrogen peroxide, sodium peracetate, sodium percarbonateand the like. Conventional redox initiator systems can also be used.Such systems are formed by combining the foregoing peroxygen compoundswith reducing agents such as sodium bisulfite, L-ascorbic acid orferrous salts.

The initiator can be present at up to about 20 mole percent based on thetotal moles of polymerizable monomers present in the oil phase. Morepreferably, the initiator is present in an amount of from about 0.001 toabout 10 mole percent based on the total moles of polymerizable monomersin the oil phase.

The polymer forming the HIPE foam structure will preferably besubstantially free of polar functional groups. This means the polymericfoam will be relatively hydrophobic in character. These hydrophobicfoams can find utility where the absorption of hydrophobic liquids isdesired. Uses of this sort include those where an oily component ismixed with water and it is desired to separate and isolate the oilycomponent, such as in the case of marine oil spills.

When these foams are to be used as absorbents for aqueous liquids suchas juice spills, milk, and the like for clean up and/or bodily liquidssuch as urine, they generally require further treatment to render thefoam relatively more hydrophilic. Hydrophilization of the foam, ifnecessary, can generally be accomplished by treating the HIPE foam witha hydrophilizing surfactant in a manner described in U.S. Pat. No.5,387,207 infra.

These hydrophilizing surfactants can be any material that enhances thewater wettability of the polymeric foam surface. They are well known inthe art, and can include a variety of surfactants, preferably of thenonionic type, such as those enumerated in U.S. Pat. No. 5,387,207infra.

Another material that is typically incorporated into the HIPE foamstructure is a hydratable, and preferably hygroscopic or deliquescent,water soluble inorganic salt. Such salts include, for example,toxicologically acceptable alkaline earth metal salts. Salts of thistype and their use with oil-soluble surfactants as the foamhydrophilizing surfactant is described in greater detail in U.S. Pat.No. 5,352,711 (DesMarais), issued Oct. 4, 1994, the disclosure of whichis incorporated by reference. Preferred salts of this type include thecalcium halides such as calcium chloride that, as previously noted, canalso be employed as the water phase electrolyte in the HIPE.

Hydratable inorganic salts can easily be incorporated by treating thefoams with aqueous solutions of such salts. These salt solutions cangenerally be used to treat the foams after completion of, or as part of,the process of removing the residual water phase from thejust-polymerized foams. Treatment of foams with such solutionspreferably deposits hydratable inorganic salts such as calcium chloridein residual amounts of at least about 0.1% by weight of the foam, andtypically in the range of from about 0.1 to about 12%.

Treatment of these relatively hydrophobic foams with hydrophilizingsurfactants (with or without hydratable salts) will typically be carriedout to the extent necessary to impart suitable hydrophilicity to thefoam. Some foams of the preferred HIPE type, however, are suitablyhydrophilic as prepared, and can have incorporated therein sufficientamounts of hydratable salts, thus requiring no additional treatment withhydrophilizing surfactants or hydratable salts. In particular, suchpreferred HIPE foams include those where certain oil phase emulsifierspreviously described and calcium chloride are used in the HIPE. In thoseinstances, the internal polymerized foam surfaces will be suitablyhydrophilic, and will include residual water-phase liquid containing ordepositing sufficient amounts of calcium chloride, even after thepolymeric foams have been dewatered to a practicable extent.

Foam preparation typically involves the steps of: 1) forming a stablehigh internal phase emulsion (HIPE); 2) polymerizing/curing this stableemulsion under conditions suitable for forming a solid polymeric foamstructure; 3) optionally washing the solid polymeric foam structure toremove the original residual water phase from the polymeric foamstructure and, if necessary, treating the polymeric foam structure witha hydrophilizing surfactant and/or hydratable salt to deposit any neededhydrophilizing surfactant/hydratable salt, and 4) thereafter dewateringthis polymeric foam structure. The procedure is described more fully inU.S. Pat. No. 5,387,207 supra.

In order to use respective materials in absorbent structures, thesematerials can be combined with other elements so as to creating an Fluidhandling member, which comprises materials according to the descriptionas laid out in the above.

Storage Absorbent Member Requirements

As described in the above the distribution members exhibit certaindesorption properties, which have to be matched by the absorptionproperties of the absorbent storage members or materials.

Thus, the storage absorbent members suitable for the present inventionexhibit high capillary suction capacities. For purposes of the presentdisclosure, this high suction capacity is measured in terms of themember's ability to uptake fluid at certain capillary heights, which aregenerally encountered when the member is positioned in an absorbentarticle. The Capillary Sorption Absorbent Capacity test (also referredto herein as the Capsorption test) measures the amount of test fluid pergram of absorbent storage member that is taken up when the storagemember is placed at varying heights on a capillary sorption apparatus.The Capillary Sorption Absorbent Capacity test is described in greaterdetail in the Test Methods section below.

In one aspect, the high capillary suction capacity storage absorbentmember suitable for the present invention has a capillary sorptionabsorbent capacity (CSAC) at a height of 35 cm of at least about 15 g/g,preferably at least about 18/g, more preferably at least about 20 g/g,still more preferably at least about 22 g/g. Typically, these storageabsorbent members will have a capillary sorption absorbent capacity at aheight of 35 cm of from about 15 g/g to about 60 g/g, more typicallyfrom about 18 g/g to about 50 g/g, still more typically from about 20g/g to about 40 g/g.

In another aspect, the high capillary suction capacity storage absorbentmember can have a CSAC at a height of 50 cm of at least about 8 g/g,preferably at least about 11 g/g, more preferably at least about 15 g/g,still more preferably at least about 19 g/g. Typically, these storageabsorbent members will have a CSAC at a height of 50 cm of from about 8g/g to about 40 g/g, more typically from about 11 g/g to about 35 g/g,still more typically from about 15 g/g to about 30 g/g.

In still another aspect, the high capillary suction capacity storageabsorbent member has a CSAC at a height of 80 cm of at least about 6g/g, preferably at least about 9 g/g, more preferably at least about 12g/g, still more preferably at least about 15 g/g. Typically, thesestorage absorbent members will have a capillary sorption absorbentcapacity at a height of 80 cm of from about 6 g/g to about 35 g/g, moretypically from about 9 g/g to about 30 g/g, still more typically fromabout 12 g/g to about 25 g/g.

In yet another aspect, the high capillary suction capacity storageabsorbent member has a CSAC at a height of 100 cm of at least about 5g/g, preferably at least about 7 g/g, more preferably at least about 10g/g, still more preferably at least about 14 g/g. Typically, thesestorage absorbent members will have a capillary sorption absorbentcapacity at a height of 100 cm of from about 5 g/g to about 30 g/g, moretypically from about 7 g/g to about 25 g/g, still more typically fromabout 10 g/g to about 20 g/g.

Though not a requirement, particularly preferred storage absorbentmembers will have an initial effective uptake rate at 200 cm of at leastabout 3 g/g/hr, more preferably at least about 4 g/g/hr, and mostpreferably at least about 8 g/g/hr. Typically, the effective uptake rateat 200 cm will be from about 3 to about 15 g/g/hr, more typically fromabout 4 to about 12 g/g/hr, still more typically from about 8 to about12 g/g/hr.

While the above minimum capillary suction capacities are important tothe storage absorbent members of the present invention, these memberswill also preferably, though not necessarily, have a capillary sorptionabsorbent capacity at zero head pressure (i.e., at 0 cm in theCapsorption test) of at least about 15 g/g. In another preferred aspect,the storage absorbent members will concurrently exhibit the required g/guptake at least two suction heights discussed above. That is, forexample, preferred storage absorbent members will have 2 or more of thefollowing properties: (i) a capillary sorption absorbent capacity (CSAC)at a height of 35 cm of at least about 10 g/g, preferably at least about13 g/g, more preferably at least about 20 g/g, still more preferably atleast about 22 g/g; (ii) a CSAC at a height of 50 cm of at least about 8g/g, preferably at least about 11 g/g, more preferably at least about 15g/g, still more preferably at least about 19 g/g; (iii) a CSAC at aheight of 80 cm of at least about 6 g/g, preferably at least about 9g/g, more preferably at least about 12 g/g, still more preferably atleast about 15 g/g; (iv) a CSAC at a height of 100 cm of at least about5 g/g, preferably at least about 7 g/g, more preferably at least about10 g/g, still more preferably at least about 14 g/g.

A yet another way to describe storage absorbent members suitable for theinvention is that the high capillary suction storage absorbent memberneeds to have a high medium absorption pressure The medium absorptionpressure of material is defined as the pressure for which the materialhas a capillary absorption efficiency of 50% and is measured in thecapillary absorption test described in the test method section, bydetermining the height at which the material will achieve 50% of it'smaximum absorption capacity in this test, and is referred to as CSAH 50.

Preferred storage absorbent members suitable for the present inventionare high capillary suction capacity storage absorbent members having acapillary sorption absorbent capacity at a height of 0 cm of at leastabout 15 g/g, preferably at least about 20 g/g, more preferably at leastabout 25g/g, most preferably at least about 35 g/g and having a mediumcapillary absorption height CSAH 50 of at least 35 cm, preferably atleast 45 cm, more preferably at least 60 cm, most preferably at least 80cm.

Materials to Achieve Storage Absorbent Member Requirements

High Surface Area Materials

The storage absorbent members useful for the present inventionpreferably comprise a high surface area material. It is this highsurface area material that provides, either itself or in combinationwith other elements such as hydrogel-forming absorbent polymer, themembers with high capillary sorption absorbent capacity. As discussedherein, high surface area materials are described, at least in oneregard, in terms of their capillary sorption absorbent capacity(measured without hydrogel-forming polymer if present in the member orany other optional material contained in the actual storage absorbentmember, such as adhesives, bonding agents, etc.). It is recognized thatmaterials having high surface areas may have uptake capacities at veryhigh suction heights (e.g., 100 cm or higher). This allows the highsurface area materials to provide one or both of the followingfunctions: i) a capillary pathway of liquid to the other absorbents,such as osmotic absorbents, and/or ii) additional absorbent capacity.Thus, while the high surface area materials may be described in terms oftheir surface area per weight or volume, Applicants herein alternativelyuse capillary sorption absorbent capacity to describe the high surfacearea material because capillary sorption absorbent capacity is aperformance parameter that generally will provide the absorbent membersfor the present invention with the requisite suction capabilities toprovide improved absorbent articles. It will be recognized that certainhigh surface area materials, e.g. glass microfibers, will themselves notexhibit particularly high capillary sorption absorbent capacity at allheights, especially very high heights (e.g., 100 cm and higher).Nonetheless, such materials may provide the desired capillary pathway ofliquid to the hydrogel-forming absorbent polymer or other absorbents toprovide the requisite capillary sorption absorbent capacities, even atrelatively high heights.

Any material having sufficient capillary sorption absorbent capacitywill be useful in the storage absorbent members of the presentinvention. In this regard, the term “high surface area material” refersto any material that itself (i.e., as measured without the osmoticabsorbent or any other optional material that makes up the storageabsorbent member) exhibits one or more of the following capillarysorption absorbent capacities: (I) A capillary sorption absorbentcapacity of at least about 2 g/g at a suction height of 100 cm,preferably at least about 3 g/g, still more preferably at least about 4g/g, and still more preferably at least about 6 g/g, at a height of 100cm; (II) A capillary sorption absorbent capacity at a height of 35 cm ofat least about 5 g/g, preferably at least about 8 g/g, more preferablyat least about 12 g/g; (III) A capillary sorption absorbent capacity ata height of 50 cm of at least about 4 g/g, preferably at least about 7g/g, more preferably at least about 9 g/g; (IV) A capillary sorptionabsorbent capacity at a height of 140 cm of at least about 1 g/g,preferably at least about 2 g/g, more preferably at least about 3 g/g,still more preferably at least about 5 g/g; or (V) A capillary sorptionabsorbent capacity at a height of 200 cm of at least about 1 g/g,preferably at least about 2 g/g, more preferably at least about 3 g/g,still more preferably at least about 5 g/g.

In one embodiment, the high surface area material will be fibrous(hereafter referred to as “high surface area fibers”) in character, soas to provide a fibrous web or fibrous matrix when combined with theother absorbent such as hydrogel-forming absorbent polymer or otherosmotic absorbent. Alternatively, and in a particularly preferredembodiment, the high surface area material will be an open-celled,hydrophilic polymeric foam (hereafter referred to as “high surface areapolymeric foams” or more generally as “polymeric foams”). Thesematerials are described in detail below.

High Surface Area Fibers

High surface area fibers useful in the present invention include thosethat are naturally occurring (modified or unmodified), as well assynthetically made fibers. The high surface area fibers have surfaceareas much greater than fibers typically used in absorbent articles,such as wood pulp fibers. The high surface area fibers used in thepresent invention will desirably be hydrophilic. As used herein, theterm “hydrophilic” describes fibers, or surfaces of fibers, that arewettable by aqueous liquids (e.g., aqueous body liquids) deposited onthese fibers. Hydrophilicity and wettability are typically defined interms of contact angle and the surface tension of the liquids and solidsinvolved. This is discussed in detail in the American Chemical Societypublication entitled Contact Angle, Wettability and Adhesion, edited byRobert F. Gould (Copyright 1964). A fiber, or surface of a fiber, issaid to be wetted by a liquid (i.e., hydrophilic) when either thecontact angle between the liquid and the fiber, or its surface, is lessthan 90°, or when the liquid tends to spread spontaneously across thesurface of the fiber, both conditions normally co-existing. Conversely,a fiber or surface is considered to be hydrophobic if the contact angleis greater than 90° and the liquid does not spread spontaneously acrossthe surface of the fiber. The hydrophilic character of the fibers usefulherein may be inherent in the fibers, or the fibers may be naturallyhydrophobic fibers that are treated to render them hydrophilic.Materials and methods for providing hydrophilic character to naturallyhydrophobic fibers are well known.

High surface area fibers useful herein will have capillary suctionspecific surface areas in the same range as the polymeric foamsdescribed below. Typically, however, high surface area fibers arecharacterized in terms of the well known BET surface area.

High surface area fibers useful herein include glass microfibers suchas, for example, glass wool available from Evanite Fiber Corp.(Corvallis, Oreg.). Glass microfibers useful herein will typically havefiber diameters of not more than about 0.8 μm, more typically from about0.1 μm to about 0.7 μm. These microfibers will have surface areas of atleast about 2 m²/g, preferably at least about 3 m²/g. Typically, thesurface area of glass microfibers will be from about 2 m²/g to about 15m²/g. Representative glass microfibers for use herein are thoseavailable from Evanite Fiber Corp. as type 104 glass fibers, which havea nominal fiber diameter of about 0.5 μm. These glass microfibers have acalculated surface area of about 3.1 m²/g.

Another type of high surface area fibers useful herein are fibrillatedcellulose acetate fibers. These fibers (referred to herein as “fibrets”)have high surface areas relative to cellulose-derived fibers commonlyemployed in the absorbent article art. Such fibrets have regions of verysmall diameters, such that their particle size width is typically fromabout 0.5 to about 5 μm. These fibrets typically have aggregate surfaceareas of about 20 m²/g. Representative fibrets useful as the highsurface area materials herein are available from Hoechst Celanese Corp.(Charlotte, N.C.) as cellulose acetate Fibrets®. For a detaileddiscussion of fibrets, including their physical properties and methodsfor their preparation, see “Cellulose Acetate Fibrets: A FibrillatedPulp With High Surface Area”, Smith, J. E., Tappi Journal, December1988, p. 237; and U.S. Pat. No. 5,486,410 (Groeger et al.) issued Jan.23, 1996; the disclosure of each of which is incorporated by referenceherein.

In addition to these fibers, the skilled artisan will recognize thatother fibers well known in the absorbency art may be modified to providehigh surface area fibers for use herein. Representative fibers that maybe modified to achieve high surface areas required by the presentinvention are disclosed in U.S. Pat. No. 5,599,335, supra (seeespecially columns 21-24).

Regardless of the nature of the high surface area fibers utilized, thefibers and the other absorbent material such as the osmotic absorbentwill be discrete materials prior to combination. As used herein, theterm “discrete” means that the high surface area fibers and the otherabsorbents are each formed prior to being combined to form the storageabsorbent member. In other words, the high surface area fibers are notformed subsequent to mixing with the other absorbent (e.g.,hydrogel-forming absorbent polymer), nor is the other absorbent formedafter combination with the high surface area fibers. Combining of thediscrete respective components ensures that the high surface area fiberswill have the desired morphology and, more importantly, the desiredsurface area.

High Surface Area Polymeric Foams

The high surface area polymeric foams useful herein are described insome respects below in terms of their physical properties. To measurecertain of these properties, it is necessary to perform analysis on thefoam in sheet form. Thus, insofar as a foam is used in particulate formand is prepared from a previously formed sheet, physical propertymeasurements will be conducted on the sheet foam (i.e., prior to formingparticulates). Where the foam is formed in situ into particles (orbeads) during the polymerization process, a similar foam (in terms ofchemical composition, cell size, W:O ratio, etc.) can be formed intosheets for the purpose of making such measurements.

High surface area polymeric foams useful in the high capillary suctionstorage absorbent members of the present invention are known in the art.Particularly preferred foams are those obtained by polymerizing a highinternal phase water-in-oil emulsion, such as those described in U.S.Pat. Nos. 5,387,207 and 5,650,222. Other particularly preferredpolymeric foams are described in more detail in co-pending U.S. patentapplication Ser. No. 09,042,429, filed Mar. 13, 1998 by T. DesMarais etal. titled “HIGH Suction Polymeric Foam Materials” (P&G Case 7052), )and co-pending U.S. patent application Ser. No. 09,042,418, filed Mar.13, 1998 by T. DesMarais et al. titled “Absorbent Materials forDistributing Aqueous Liquids” (P&G Case 7051), the disclosure of each ofwhich is incorporated by reference herein. (Specific preferred foamsdescribed in one or both of these copending applications are describedin the Examples section below.) Polymeric foams useful herein are thosewhich are relatively open-celled. This means many of the individualcells of the foam are in unobstructed communication with adjoiningcells. The cells in such relatively open-celled foam structures haveintercellular openings or “windows” that are large enough to permitready liquid transfer from one cell to the other within the foamstructure.

These relatively open-celled foam structures will generally have areticulated character with the individual cells being defined by aplurality of mutually connected, three dimensionally branched webs. Thestrands of polymeric material making up these branched webs can bereferred to as “struts.” For purposes of the present invention, a mostpreferred foam material will have at least about 80% of the cells in thefoam structure that are at least 1 μm in size in liquid communicationwith at least one adjacent cell.

In addition to being open-celled, these polymeric foams are sufficientlyhydrophilic to permit the foam to absorb aqueous liquids. The internalsurfaces of the foam structures are rendered hydrophilic by residualhydrophilizing surfactants left in the foam structure afterpolymerization, or by selected post-polymerization foam treatmentprocedures, as described hereafter.

The extent to which these polymeric foams are “hydrophilic” can bequantified by the “adhesion tension” value exhibited when in contactwith an absorbable test liquid. The adhesion tension exhibited by thesefoams can be determined experimentally using a procedure where weightuptake of a test liquid, e.g., synthetic urine, is measured for a sampleof known dimensions and capillary suction specific surface area. Such aprocedure is described in greater detail in the Test Methods section ofU.S. Pat. No. 5,387,207, infra. Foams which are useful high surface areamaterials in the present invention are generally those which exhibit anadhesion tension value of from about 15 to about 65 dynes/cm, morepreferably from about 20 to about 65 dynes/cm, as determined bycapillary absorption of synthetic urine having a surface tension of 65±5dynes/cm.

The polymeric foams useful herein are preferably prepared in the form ofcollapsed (i.e., unexpanded), polymeric foams that, upon contact withaqueous liquids, absorb such liquids and expand when the amount absorbedlowers the combined capillary pressure plus confining pressure to belowthe expansion pressure (described below) of the foam. These collapsedpolymeric foams are usually obtained by expressing the water phase fromthe polymerized HIPE foam through compressive forces, and/or thermaldrying and/or vacuum dewatering. After compression, and/or thermaldrying/vacuum dewatering, these polymeric foams are in a collapsed, orunexpanded state.

The cellular structure of a representative collapsed HIPE foam fromwhich water has been expressed by compression is shown in thephotomicrograph of FIGS. 3 and 4 of U.S. Pat. No. 5,650,222, discussedabove. As shown in these figures, the cellular structure of the foam isdistorted, especially when compared to the expanded HIPE foam structuresshown in FIGS. 1 and 2 of the '222 patent. As can also be seen in FIGS.3 and 4 of the '222 patent, the voids or pores (dark areas) in thecollapsed foam structure have been flattened or elongated. (It is notedthat the foams depicted in the '222 patent are in sheet form; asdiscussed below, while foams in sheet forms are useful herein, in apreferred embodiment, the foam will be in particulate form.) Thecellular structure of another HIPE-derived foam (in its expanded state)useful herein is depicted in FIGS. 3 and 4 herein. The preparation ofthis particular foam and related foams are described herein in Examples2 through 4, and these very high surface area foams are described inmore detail in co-pending U.S. patent application Ser. No. 09,042,429,filed Mar. 13, 1998 by T. DesMarais et al. titled “High SuctionPolymeric Foam Materials” (P&G Case 7052), ) and co-pending U.S. patentapplication Ser. No 09,042,418, filed Mar. 13, 1998 by T. DesMarais etal. titled “Absorbent Materials for Distributing Aqueous Liquids” (P&GCase 7051), the disclosure of each of which is incorporated by referenceherein.

Following compression and/or thermal drying/vacuum dewatering, thecollapsed polymeric foam may reexpand when wetted with aqueous liquids.Surprisingly, these polymeric foams remain in this collapsed, orunexpanded, state for significant periods of time, e.g., up to at leastabout 1 year. The ability of these polymeric foams to remain in thiscollapsed/unexpanded state is believed to be due to capillary forces,and in particular the capillary pressures developed within the foamstructure. As used herein, “capillary pressures” refers to the pressuredifferential across the liquid/air interface due to the curvature ofmeniscus within the narrow confines of the pores in the foam. [SeeChatterjee, “Absorbency,” Textile Science and Technology, Vol. 7, 1985,p. 36.]

After compression, and/or thermal drying/vacuum dewatering to apracticable extent, these polymeric foams have residual water thatincludes both the water of hydration associated with the hygroscopic,hydrated salt incorporated therein, as well as free water absorbedwithin the foam. This residual water (assisted by the hydrated salts) isbelieved to exert capillary pressures on the resulting collapsed foamstructure. Collapsed polymeric foams of the present invention can haveresidual water contents of at least about 4%, typically from about 4 toabout 40%, by weight of the foam when stored at ambient conditions of72° F. (22° C.) and 50% relative humidity. Preferred collapsed polymericfoams have residual water contents of from about 5 to about 30% byweight of the foam.

A key parameter of these foams is their glass transition temperature.The Tg represents the midpoint of the transition between the glassy andrubbery states of the polymer. Foams that have a higher Tg than thetemperature of use can be very strong but will also be rigid andpotentially prone to fracture. Such foams also typically take a longtime to recover to the expanded state when wetted with aqueous liquidscolder than the Tg of the polymer after having been stored in thecollapsed state for prolonged periods. The desired combination ofmechanical properties, specifically strength and resilience, typicallynecessitates a fairly selective range of monomer types and levels toachieve these desired properties.

For foams useful in the present invention, the Tg should be as low aspossible, so long as the foam has acceptable strength at in-usetemperatures. Accordingly, monomers are selected as much as possiblethat provide corresponding homopolymers having lower Tg's. It has beenfound that the chain length of the alkyl group on the acrylate andmethacrylate comonomers can be longer than would be predicted from theTg of the homologous homopolymer series. Specifically, it has been foundthat the homologous series of alkyl acrylate or methacrylatehomopolymers have a minimum Tg at a chain length of 8 carbon atoms. Bycontrast, the minimum Tg of the copolymers of the present inventionoccurs at a chain length of about 12 carbon atoms. (While the alkylsubstituted styrene monomers can be used in place of the alkyl acrylatesand methacrylates, their availability is currently extremely limited).

The shape of the glass transition region of the polymer can also beimportant, i.e., whether it is narrow or broad as a function oftemperature. This glass transition region shape is particularly relevantwhere the in-use temperature (usually ambient or body temperature) ofthe polymer is at or near the Tg. For example, a broader transitionregion can mean an incomplete transition at in-use temperatures.Typically, if the transition is incomplete at the in-use temperature,the polymer will evidence greater rigidity and will be less resilient.Conversely, if the transition is completed at the in-use temperature,then the polymer will exhibit faster recovery from compression whenwetted with aqueous liquids. Accordingly, it is desirable to control theTg and the breadth of the transition region of the polymer to achievethe desired mechanical properties. Generally, it is preferred that theTg of the polymer be at least about 10° C. lower than the in-usetemperature. (The Tg and the width of the transition region are derivedfrom the loss tangent vs. temperature curve from a dynamic mechanicalanalysis (DMA) measurement, as described in the Test Methods section ofU.S. Pat. No. 5,650,222).

While the high surface area materials in general have been described interms of their capillary sorption absorbent capacity, the high surfacearea polymeric foams useful herein may also be described in terms oftheir capillary suction specific surface area (hereafter referred to as“CSSSA”). In general, CSSSA is a measure of the test-liquid-accessiblesurface area of the polymeric network forming a particular foam per unitmass of the bulk foam material (polymer structural material plus solidresidual material). Capillary suction specific surface area isdetermined both by the dimensions of the cellular units in the foam andby the density of the polymer, and is thus a way of quantifying thetotal amount of solid surface provided by the foam network to the extentthat such a surface participates in absorbency. For purposes ofcharacterizing the foams useful herein, CSSSA is measured on a sheet ofthe foam in question, even where the foam is in particle form whenincorporated in a storage absorbent member.

The CSSSA of a foam is particularly relevant to whether the foam willprovide the requisite capillary suction for use in preparing storageabsorbent members of the present invention. This is because thecapillary pressure developed within the foam structure is proportionalto the capillary suction specific surface area. In addition, the CSSSAis relevant to whether adequate capillary pressures are developed withinthe foam structure to keep it in a collapsed state until wetted withaqueous liquids. Assuming other factors such as the foam density andadhesion tension are constant, this means that, as the CSSSA isincreased (or decreased), the capillary pressure within the foamstructure also increases (or decreases) proportionately.

For purposes of the present invention, CSSSA is determined by measuringthe amount of capillary uptake of a low surface tension liquid (e.g.,ethanol) which occurs within a foam sample of a known mass anddimensions. A detailed description of such a procedure for determiningfoam specific surface area is set forth in the Test Methods section ofU.S. Pat. No. 5,387,207, which is incorporated by reference. Anyreasonable alternative method for determining CSSSA can also beutilized.

The collapsed polymeric foams of the present invention useful asabsorbents are those that have a CSSSA of at least about 3 m²/g.Typically, the CSSSA is in the range from about 3 to about 30 m²/g,preferably from about 4 to about 17 m²/g, most preferably from about 5to about 15 m²/g. Foams having such CSSSA values (with expanded statedensities of from about 0.010 to about 0.033 g/cm³) will generallypossess an especially desirable balance of absorbent capacity,liquid-retaining and liquid-wicking or distribution characteristics foraqueous liquids such as urine. In addition, foams having such CSSSA candevelop a sufficient capillary pressure to keep the foam in a collapsed,unexpanded state until wetted with such aqueous liquids.

As discussed above, for particularly preferred collapsable polymericfoams, in their collapsed state the capillary pressures developed withinthe foam structure at least equal the forces exerted by the elasticrecovery or modulus of the compressed polymer. In other words, thecapillary pressure necessary to keep the collapsed foam relatively thinis determined by the countervailing force exerted by the compressedpolymeric foam as it tries to “spring back.” The elastic recoverytendency of polymeric foams can be estimated from stress-strainexperiments where the expanded foam is compressed to about ⅙ (17%) ofits original, expanded thickness and then held in this compressed stateuntil a relaxed stress value is measured. Alternatively, and for thepurposes of the present invention, the relaxed stress value is estimatedfrom measurements on the polymeric foam in its collapsed state when incontact with aqueous liquids, e.g., water. This alternative relaxedstress value is hereafter referred to as the “expansion pressure” of thefoam. The expansion pressure for collapsed polymeric foams of thepresent invention is about 50 kiloPascals (kPa) or less and typicallyfrom about 7 to about 40 kPa. A detailed description of a procedure forestimating the expansion pressure of foams is set forth in the TestMethods section of U.S. Pat. No. 5,387,207.

Another important property of the high surface area polymeric foamsuseful in the present invention is their free absorbent capacity. “Freeabsorbent capacity” (or “FAC”) is the total amount of test liquid(synthetic urine) which a given foam sample will absorb into itscellular structure per unit mass of solid material in the sample. To beespecially useful in the storage absorbent members of the presentinvention, the polymeric foams should have a free absorbent capacity offrom about 30 to about 100 ml, preferably from about 30 to about 75 mlof synthetic urine per gram of dry foam material. The procedure fordetermining the free absorbent capacity of the foam is describedhereafter in the Test Methods section of U.S. Pat. No. 5,650,222.

Upon exposure to aqueous liquids, preferred collapsed polymeric foamsabsorb the liquids and expand. The polymeric foams, in their expandedstate, absorb more liquid than most other foams. The “expansion factor”for these foams is at least about 4×, i.e. the thickness of the foam inits expanded state is at least about 4 times the thickness of the foamin its collapsed state. The collapsed foams preferably have an expansionfactor in the range of from about 4× to about 15×, more preferably fromabout 5× to about 10×.

For the purposes of the present invention, the relationship betweenexpanded and collapsed thickness for compressively dewatered foams canbe empirically predicted from the following equation:

thickness_(expanded)=thickness_(collapsed)×((0.133×W:O ratio)±2)

where:

thickness_(expanded) is the thickness of the foam in its expanded state;

thickness_(collapsed) is the thickness of the foam in its collapsedstate;

and W:O ratio is the water-to-oil ratio of the HIPE from which the foamis made. Thus, a typical polymeric foam made from an emulsion with awater-to-oil ratio of 60:1 would have a predicted expansion factor of8.0, i.e., an expanded thickness 8 times the collapsed thickness of thefoam.

The procedure for measuring the expansion factor is described hereafterin the Test Methods section of U.S. Pat. No. 5,650,222.

A relevant mechanical feature of the high surface area polymeric foamsuseful in the present invention is their strength in their expandedstate, as determined by resistance to compression deflection (RTCD). TheRTCD exhibited by the foams herein is a function of the polymer modulus,as well as the density and structure of the foam network. The polymermodulus is, in turn, determined by: a) the polymer composition; b) theconditions under which the foam is polymerized (for example, thecompleteness of polymerization obtained, specifically with respect tocrosslinking); and c) the extent to which the polymer is plasticized byresidual material, e.g., emulsifiers, left in the foam structure afterprocessing.

To be useful as the high surface area portion of the absorbent membersof the present invention, the polymeric foams should be suitablyresistant to deformation or compression by forces encountered in use.Foams which do not possess sufficient foam strength in terms of RTCD mayprovide the requisite capillary suction capacity under no-loadconditions but will not provide those capacities under the compressivestress caused by the motion and activity of the user of the absorbentarticles that contain the foam.

The RTCD exhibited by the polymeric foams useful in the presentinvention can be quantified by determining the amount of strain producedin a sample of saturated foam held under a certain confining pressurefor a specified temperature and period of time. The method for carryingout this particular type of test is described hereafter in the TestMethods section of U.S. Pat. No. 5,650,222. Foams useful herein willpreferably exhibit a RTCD such that a confining pressure of 5.1 kPaproduces a strain of typically about 90% or less compression of the foamstructure when it has been saturated to its free absorbent capacity withsynthetic urine having a surface tension of 65±5 dynes/cm. Preferablythe strain produced under such conditions will be in the range fromabout 1 to about 90%, more preferably from about 1 to about 25%, stillmore preferably from about 2 to about 10%, still more preferably fromabout 2 to about 5%.

The high surface area polymeric foams useful herein can be also bedescribed in terms of their vertical hang sorption height (hereafter“VHSH”). The VHSH height at X % is the height in cm where X % of the 0cm capacity (or FAC) is retained in the foam. A typical value ofimportance is the VHSH at 90%, though in principle X may be any value.The most reproducible measure for VHSH is achieved at X=90%, within theexperience of the inventors. It will be obvious to one skilled in theart that this single point value does not fully express the shape of thecurve obtained in a plot of capacity vs. height. The single pointhowever serves as a practical point of comparison for the foams usefulherein. In this regard, the foams will typically have an equilibrium 90%VHSH of at least about 20 cm, preferably at least about 40 cm, stillmore preferably at least about 60 cm, still more preferably at leastabout 70 cm and still more preferably at least about 80 cm. Typically,preferred polymeric foams will have a 90% VHSH of from about 20 to about90 cm, more typically from about 60 to about 90 cm, more typically fromabout 70 to about 90 cm, still more typically from, about 80 to about 90cm. The method for measuring 90% VHSH is described in detail in the TestMethods section below. As indicated, where the high surface areapolymeric foam is in particulate form when combined with the otherabsorbent, such as an osmotic absorbent, 90% VHSH is measured on thecorresponding foam in sheet form (i.e., prior to forming particulates).Where the foam is formed into particles (or beads) during thepolymerization process, a similar foam can be formed into sheets forassessing the foam's 90% VHSH.

Foam cells, and especially cells that are formed by polymerizing amonomer-containing oil phase that surrounds relatively monomer-freewater-phase droplets, will frequently be substantially spherical inshape. The size or “diameter” of such spherical cells is a commonly usedparameter for characterizing foams in general. Since cells in a givensample of polymeric foam will not necessarily be of approximately thesame size, an average cell size, i.e., average cell diameter, will oftenbe specified.

A number of techniques are available for determining the average cellsize of foams. The most useful technique, however, for determining cellsize in foams involves a simple measurement based on the scanningelectron photomicrograph of a foam sample.

The cell size measurements given herein are based on the number averagecell size of the foam in its expanded state, e.g., as shown in FIG. 1 ofU.S. Pat. No. 5,650,222. The foams useful in accordance with the presentinvention will preferably have a number average cell size of about 80 μmor less, and typically from about 5 to about 50 μm. “Foam density”(i.e., in grams of foam per cubic centimeter of foam volume in air) isspecified herein on a dry basis. The amount of absorbed water-solubleresidual materials, e.g., residual salts and liquid left in the foam,for example, after HIPE polymerization, washing and/or hydrophilization,is disregarded in calculating and expressing foam density. Foam densitydoes include, however, other water-insoluble residual materials such asemulsifiers present in the polymerized foam. Such residual materialscan, in fact, contribute significant mass to the foam material.

Any suitable gravimetric procedure that will provide a determination ofmass of solid foam material per unit volume of foam structure can beused to measure foam density. For example, an ASTM gravimetric proceduredescribed more fully in the Test Methods section of U.S. Pat. No.5,387,207 (Dyer et al.) issued Feb. 7, 1995, supra, is one method thatcan be employed for density determination. In their collapsed state,polymeric foams useful in the present invention have dry basis densityvalues (exclusive of any residual salts and or water) in the range offrom about 0.1 to about 0.2 g/cm³, preferably from about 0.11 to about0.19 g/cm³, and most preferably from about 0.12 to about 0.17 g/cm³. Intheir expanded state, polymeric foams useful herein will have dry basisdensity values in the range of from about 0.01 to about 0.033 g/cm³,preferably from about 0.013 to about 0.033 g/cm³.

Vertical wicking, i.e., liquid wicking in a direction opposite fromgravitational force, is a desirable performance attribute for polymericfoams useful herein. For the purposes of this invention, verticalwicking rate is reflective of the permeability of the material, andthus, the ability of the material to deliver liquid to the otherabsorbent, such as a hydrogel-forming absorbent polymer or other osmoticabsorbent.

Vertical wicking rate is determined by measuring the time taken for acolored test liquid (e.g., synthetic urine) in a reservoir to wick avertical distance of 5 cm through a test strip of foam of specifiedsize. The vertical wicking procedure is described in greater detail inthe Test Methods section of U.S. Pat. No. 5,387,207, but is performed at31° C., instead of 37° C. To be especially useful in absorbent membersfor absorbing urine, the foams useful herein will preferably wicksynthetic urine ( 65±5 dynes/cm) to a height of 5 cm in no more thanabout 15 minutes. More preferably, the preferred foam absorbents of thepresent invention wick synthetic urine to a height of 5 cm in no morethan about 10 minutes.

The vertical wicking absorbent capacity test measures the amount of testliquid per gram of absorbent foam that is held within each one in. (2.54 cm) vertical section of the same standard size foam sample used inthe vertical wicking test. Such a determination is generally made afterthe sample has been allowed to vertically wick test liquid toequilibrium (e.g., after about 18 hours). Like the vertical wickingtest, the vertical wicking absorbent capacity test is described ingreater detail in the Test Methods section of U.S. Pat. No. 5,387,207(Dyer et al.) issued Feb. 7, 1995, supra. High vertical wickingabsorbent capacities at high heights are theoretically equivalent tohigh capillary sorption absorbent capacities at high heights. Since thesheet form of the foams useful herein is amenable to the former test andthe former test is more easily and cheaply performed, the data from theformer test are recommended as the means of characterizing thisimportant parameter of the foams of this invention.

While high capillary suction foams may be in sheet form when combinedwith other absorbent such as osmotic absorbent (e.g., hydrogel-formingabsorbent polymer), in a particularly preferred embodiment, thepolymeric foam will be in particle form and will be mixed with particlesof hydrogel-forming polymer to provide a blend. That is, while the foammay initially be prepared in sheet form, these sheets may be processedto provide particles of foam, which are then combined with thehydrogelling polymer. As discussed above, the foams useful herein, andprocesses for their preparation, are described in great detail in U.S.Pat. Nos. 5,387,207, 5,650,222, co-pending U.S. patent application Ser.No. 09,042,429, filed Mar. 13,1998 by T. DesMarais et al. titled “HighSuction Polymeric Foam Materials” (P&G Case 7052), and co-pending U.S.patent application Ser. No. 09,042,418, filed Mar. 13, 1998 by T.DesMarais et al. titled “Absorbent Materials for Distributing AqueousLiquids” (P&G Case 7051). Foam particles may be prepared by firstforming a sheet of foam per the teachings of these references, followedby mechanical processing the foam to provide particles (e.g.,pulverizing, cutting, chopping, etc.) of the desired dimension.Alternatively, foam particles may be prepared directly from emulsion inthe form of polymeric microbeads, as described in U.S. Pat. No.5,653,922, issued Aug. 5, 1997 to Li et al., and U.S. Pat. No.5,583,162, issued Dec. 10, 1996 to Li et al., the disclosure of each ofwhich is incorporated by reference herein. Specific embodiments formaking polymer foam/hydrogel-forming polymer blends are discussed inmore detail below.

Applicants have also found that the high surface area foams mayoptionally comprise a fluid so as to provide increased transfer of urineto the other absorbent or osmotic absorbent of the storage absorbentmember. The pre-wetting fluid partially fills the polymeric foam and,without wishing to be held to a particular theory, increases the uptakerate of the foam. Ideally, polymeric foam comprising pre-wettingfluid(s) should be shelf stable, with sufficiently low water activity toprevent microbial growth and prevent evaporative water loss and notmigrate out of the foam over time. Water can be used as a pre-wettingfluid to provide the absorption performance but may not by itself meetthe other requirements.

Hydrogel-Forming Absorbent Polymers

The storage absorbent members of the present invention furtherpreferably comprise at least one hydrogel-forming absorbent polymer(also referred to as hydrogel-forming polymer). Hydrogel-formingpolymers useful in the present invention include a variety ofwater-insoluble, but water-swellable polymers capable of absorbing largequantities of liquids. Such hydrogel-forming polymers are well known inthe art and any of these materials are useful in the high capillarysuction absorbent members of the present invention.

Hydrogel-forming absorbent polymers materials are also commonly referredto as “hydrocolloids,” or “superabsorbent” materials and can includepolysaccharides such as carboxymethyl starch, carboxymethyl cellulose,and hydroxypropyl cellulose; nonionic types such as polyvinyl alcohol,and polyvinyl ethers; cationic types such as polyvinyl pyridine,polyvinyl morpholinione, and N,N-dimethylaminoethyl orN,N-diethylaminopropyl acrylates and methacrylates, and the respectivequaternary salts thereof. Typically, hydrogel-forming absorbent polymersuseful in the present invention have a multiplicity of anionic,functional groups, such as sulfonic acid, and more typically carboxy,groups. Examples of polymers suitable for use herein include those whichare prepared from polymerizable, unsaturated, acid-containing monomers.Thus, such monomers include the olefinically unsaturated acids andanhydrides that contain at least one carbon to carbon olefinic doublebond. More specifically, these monomers can be selected fromolefinically unsaturated carboxylic acids and acid anhydrides,olefinically unsaturated sulfonic acids, and mixtures thereof. Asindicated above, the nature of the hydrogel-forming absorbent polymer isnot critical to the members of the present invention. Nonetheless, theselection of the optimal polymeric material may enhance the performancecharacteristics of the present members. The disclosure that followsdescribes preferred properties of the absorbent polymers useful herein.These properties should not be interpreted as limitations; rather, theymerely indicate the progression that has occurred in the absorbentpolymer art over the past several years.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the hydrogel-forming absorbent polymers herein. Suchnon-acid monomers can include, for example, the water-soluble orwater-dispersible esters of the acid-containing monomers, as well asmonomers that contain no carboxylic or sulfonic acid groups at all.Optional non-acid monomers can thus include monomers containing thefollowing types of functional groups: carboxylic acid or sulfonic acidesters, hydroxyl groups, amide-groups, amino groups, nitrile groups,quaternary ammonium salt groups, aryl groups (e.g., phenyl groups, suchas those derived from styrene monomer). These non-acid monomers arewell-known materials and are described in greater detail, for example,in U.S. Pat. No. 4,076,663 (Masuda et al.), issued Feb. 28, 1978, and inU.S. Pat. No. 4,062,817 (Westerman), issued Dec. 13, 1977, both of whichare incorporated by reference.

Olefinically unsaturated carboxylic acid and carboxylic acid anhydridemonomers include the acrylic acids typified by acrylic acid itself,methacrylic acid, ethacrylic acid, α-chloroacrylic acid, a-cyanoacrylicacid, β-methylacrylic acid (crotonic acid), α-phenylacrylic acid,β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelicacid, cinnamic acid, p-chlorocinnamic acid, β-sterylacrylic acid,itaconic acid, citroconic acid, mesaconic acid, glutaconic acid,aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleicacid anhydride.

Olefinically unsaturated sulfonic acid monomers include aliphatic oraromatic vinyl sulfonic acids such as vinylsulfonic acid, allyl sulfonicacid, vinyl toluene sulfonic acid and styrene sulfonic acid; acrylic andmethacrylic sulfonic acid such as sulfoethyl acrylate, sulfoethylmethacrylate, sulfopropyl acrylate, sulfopropyl methacrylate,2-hydroxy-3-methacryloxypropyl sulfonic acid and2-acrylamide-2-methylpropane sulfonic acid.

Preferred hydrogel-forming absorbent polymers for use in the presentinvention contain carboxy groups. These polymers include hydrolyzedstarch-acrylonitrile graft copolymers, partially neutralized hydrolyzedstarch- acrylonitrile graft copolymers, starch-acrylic acid graftcopolymers, partially neutralized starch-acrylic acid graft copolymers,saponified vinyl acetate-acrylic ester copolymers, hydrolyzedacrylonitrile or acrylamide copolymers, slightly network crosslinkedpolymers of any of the foregoing copolymers, partially neutralizedpolyacrylic acid, and slightly network crosslinked polymers of partiallyneutralized polyacrylic acid. These polymers can be used either solelyor in the form of a mixture of two or more different polymers. Examplesof these polymer materials are disclosed in U.S. Pat. Nos. 3,661,875,4,076,663, 4,093,776, 4,666,983, and 4,734,478.

Most preferred polymer materials for use in making the hydrogel-formingabsorbent polymers are slightly network crosslinked polymers ofpartially neutralized polyacrylic acids and starch derivatives thereof.Most preferably, the hydrogel-forming absorbent polymers comprise fromabout 50 to about 95%, preferably about 75%, neutralized, slightlynetwork crosslinked, polyacrylic acid (i.e., poly (sodiumacrylate/acrylic acid)). Network crosslinking renders the polymersubstantially water-insoluble and, in part, determines the absorptivecapacity and extractable polymer content characteristics of thehydrogel-forming absorbent polymers. Processes for network crosslinkingthese polymers and typical network crosslinking agents are described ingreater detail in U.S. Pat. No. 4,076,663.

While the hydrogel-forming absorbent polymer is preferably of one type(i.e., homogeneous), mixtures of polymers can also be used in thepresent invention. For example, mixtures of starch-acrylic acid graftcopolymers and slightly network crosslinked polymers of partiallyneutralized polyacrylic acid can be used in the present invention.

The hydrogel-forming polymer component may also be in the form of amixed-bed ion-exchange composition comprising a cation-exchangehydrogel-forming absorbent polymer and an anion-exchangehydrogel-forming absorbent polymer. Such mixed-bed ion-exchangecompositions are described in, e.g., PCT Publication WO 99/34843 byHird, et al. (P&G Case 6975—titled “Absorbent Polymer CompositionsHaving High Sorption Capacities Under an Applied Pressure”); PCTPublication WO 99/34841 by Ashraf, et al. (P&G Case 6976—titled“Absorbent Polymer Compositions with High Sorption Capacity and HighFluid Permeability Under an Applied Pressure”); and U.S. Pat. No.6,121,509, filed Jan. 7, 1998 by Ashraf, et al. (P&G Case 6977—titled“Absorbent Polymer Compositions Having High Sorption Capacities Under anApplied Pressure and Improved Intergrity in the Swollen State”); thedisclosure of each of which is incorporated herein by reference.

The hydrogel-forming absorbent polymers useful in the present inventioncan have a size, shape and/or morphology varying over a wide range.These polymers can be in the form of particles that do not have a largeratio of greatest dimension to smallest dimension (e.g., granules,pulverulents, interparticle aggregates, interparticle crosslinkedaggregates, and the like) and can be in the form of fibers, sheets,films, foams, flakes and the like. The hydrogel-forming absorbentpolymers can also comprise mixtures with low levels of one or moreadditives, such as for example powdered silica, surfactants, glue,binders, and the like. The components in this mixture can be physicallyand/or chemically associated in a form such that the hydrogel-formingpolymer component and the non-hydrogel-forming polymer additive are notreadily physically separable.

The hydrogel-forming absorbent polymers can be essentially non-porous(i.e., no internal porosity) or have substantial internal porosity.

For particles as described above, particle size is defined as thedimension determined by sieve size analysis. Thus, for example, aparticle that is retained on a U.S.A. Standard Testing Sieve with 710micron openings (e.g., No. 25 U.S. Series Alternate Sieve Designation)is considered to have a size greater than 710 microns; a particle thatpasses through a sieve with 710 micron openings and is retained on asieve with 500 micron openings (e.g., No. 35 U.S, Series Alternate SieveDesignation) is considered to have a particle size between 500 and 710μm; and a particle that passes through a sieve with 500 micron openingsis considered to have a size less than 500 μm. The mass median particlesize of a given sample of hydrogel-forming absorbent polymer particlesis defined as the particle size that divides the sample in half on amass basis, i.e., one-half of the sample by weight will have a particlesize less than the mass median size and one-half of the sample will havea particle size greater than the mass median size. A standardparticle-size plotting method (wherein the cumulative weight percent ofthe particle sample retained on or passed through a given sieve sizeopening is plotted versus sieve size opening on probability paper) istypically used to determine mass median particle size when the 50% massvalue does not correspond to the size opening of a U.S.A. StandardTesting Sieve. These methods for determining particle sizes of thehydrogel-forming absorbent polymer particles are further described inU.S. Pat. No. 5,061,259 (Goldman et al.), issued Oct. 29, 1991, which isincorporated by reference.

For particles of hydrogel-forming absorbent polymers useful in thepresent invention, the particles will generally range in size from about1 to about 2000 μm, more preferably from about 20 to about 1000 μm. Themass median particle size will generally be from about 20 to about 1500μm, more preferably from about 50 μm to about 1000 μm, and even morepreferably from about 100 to about 800 μm.

Where relatively high concentrations (e.g. 40%, 60%, or greater, byweight) of hydrogel forming absorbent polymer are utilized in theabsorbent members of the present invention, still other properties ofthe absorbent polymer may be relevant. In such embodiments, thematerials may have one or more of the properties described by U.S. Pat.No. 5,562,646, issued Oct. 8, 1996 to Goldman et al. and U.S. Pat. No.5,599,335, issued Feb. 4, 1997 to Goldman et al., the disclosure of eachof which is incorporated by reference herein.

The basic hydrogel-forming absorbent polymer can be formed in anyconventional manner. Typical and preferred processes for producing thesepolymers are described in U.S. Reissue Patent 32,649 (Brandt et al.),issued Apr. 19, 1988, U.S. Pat. No. 4,666,983 (Tsubakimoto et al.),issued May 19, 1987, and U.S. Pat. No. 4,625,001 (Tsubakimoto et al.),issued Nov. 25, 1986, all of which are incorporated by reference.

Preferred methods for forming the basic hydrogel-forming absorbentpolymer are those involving aqueous solution or other solutionpolymerization methods. As described in the above-referenced U.S. PatentReissue 32,649, aqueous solution polymerization involves the use of anaqueous reaction mixture to carry out polymerization. The aqueousreaction mixture is then subjected to polymerization conditions whichare sufficient to produce in the mixture, substantially water-insoluble,slightly network crosslinked polymer. The mass of polymer formed canthen be pulverized or chopped to form individual particles.

More specifically, the aqueous solution polymerization method forproducing the hydrogel-forming absorbent polymer comprises thepreparation of an aqueous reaction mixture in which to carry out thepolymerization. One element of such a reaction mixture is the acidgroup-containing monomer that will form the “backbone” of thehydrogel-forming absorbent polymer to be produced. The reaction mixturewill generally comprise about 100 parts by weight of the monomer.Another component of the aqueous reaction mixture comprises a networkcrosslinking agent. Network crosslinking agents useful in forming thehydrogel-forming absorbent polymer according to the present inventionare described in more detail in the above-referenced U.S. Reissue Pat.No. 32,649, U.S. Pat. Nos. 4,666,983, and 4,625,001. The networkcrosslinking agent will generally be present in the aqueous reactionmixture in an amount of from about 0.001 mole percent to about 5 molepercent based on the total moles of monomer present in the aqueousmixture (about 0.01 to about 20 parts by weight, based on 100 parts byweight of the monomer). An optional component of the aqueous reactionmixture comprises a free radical initiator including, for example,peroxygen compounds such as sodium, potassium, and ammonium persulfates,caprylyl peroxide, benzoyl peroxide, hydrogen peroxide, cumenehydroperoxides, tertiary butyl diperphthalate, tertiary butylperbenzoate, sodium peracetate, sodium percarbonate, and the like. Otheroptional components of the aqueous reaction mixture comprise the variousnon-acidic co-monomers, including esters of the essential unsaturatedacidic functional group-containing monomers or other co-monomerscontaining no carboxylic or sulfonic acid functionalities at all.

The aqueous reaction mixture is subjected to polymerization conditionswhich are sufficient to produce in the mixture substantiallywater-insoluble, but water-swellable, hydrogel-forming absorbentslightly network crosslinked polymers. The polymerization conditions arealso discussed in more detail in the three above-referenced patents.Such polymerization conditions generally involve heating (thermalactivation techniques) to a polymerization temperature from about 0° toabout 100° C., more preferably from about 5° to about 40° C.Polymerization conditions under which the aqueous reaction mixture ismaintained can also include, for example, subjecting the reactionmixture, or portions thereof, to any conventional form of polymerizationactivating irradiation. Radioactive, electronic, ultraviolet, orelectromagnetic radiation are alternative conventional polymerizationtechniques.

The acid functional groups of the hydrogel-forming absorbent polymerformed in the aqueous reaction mixture are also preferably neutralized.Neutralization can be carried out in any conventional manner thatresults in at least about 25 mole percent, and more preferably at leastabout 50 mole percent, of the total monomer utilized to form the polymerbeing acid group-containing monomers that are neutralized with asalt-forming cation. Such salt-forming cations include, for example,alkali metals, ammonium, substituted ammonium and amines as discussed infurther detail in the above-references U.S. Reissue Pat. No. 32,649.

While it is preferred that the particulate versions of hydrogel-formingabsorbent polymer be manufactured using an aqueous solutionpolymerization process, it is also possible to carry out thepolymerization process using multi-phase polymerization processingtechniques such as inverse emulsion polymerization or inverse suspensionpolymerization procedures. In the inverse emulsion polymerization orinverse suspension polymerization procedures, the aqueous reactionmixture as described before is suspended in the form of tiny droplets ina matrix of a water-immiscible, inert organic solvent such ascyclohexane. The resultant particles of hydrogel-forming absorbentpolymer are generally spherical in shape. Inverse suspensionpolymerization procedures are described in greater detail in U.S. Pat.No. 4,340,706 (Obaysashi et al.), issued Jul. 20, 1982, U.S. Pat. No.4,506,052 (Flesher et al.), issued Mar. 19, 1985, and U.S. Pat. No.4,735,987 (Morita et al.), issued Apr. 5, 1988, all of which areincorporated by reference.

Surface crosslinking of the initially formed polymers is a preferredprocess for obtaining hydrogel-forming absorbent polymers havingrelatively high porosity hydrogel-layer (“PHL”), performance underpressure (“PUP”) capacity and saline flow conductivity (“SFC”) values,which may be beneficial in the context of the present invention.Suitable general methods for carrying out surface crosslinking ofhydrogel-forming absorbent polymers according to the present inventionare disclosed in U.S. Pat. No. 4,541,871 (Obayashi), issued Sep. 17,1985; published PCT application WO92/16565 (Stanley), published Oct. 1,1992, published PCT application WO90/08789 (Tai), published Aug. 9,1990; published PCT application WO93/05080 (Stanley), published Mar. 18,1993; U.S. Pat. No. 4,824,901 (Alexander), issued Apr. 25, 1989; U.S.Pat. No. 4,789,861 (Johnson), issued Jan. 17, 1989; U.S. Pat. No.4,587,308 (Makita), issued May 6, 1986; U.S. Pat. No. 4,734,478(Tsubakimoto), issued Mar. 29, 1988; U.S. Pat. No. 5,164,459 (Kimura etal.), issued Nov. 17, 1992; published German patent application4,020,780 (Dahmen), published Aug. 29, 1991; and published Europeanpatent application 509,708 (Gartner), published Oct. 21, 1992; all ofwhich are incorporated by reference. See also, U.S. Pat. No. 5,562,646(Goldman et al.), issued Oct. 8, 1996, and U.S. Pat. No. 5,599,335(Goldman et al.), issued Feb. 4, 1997.

The hydrogel-forming absorbent polymer particles prepared according tothe present invention are typically substantially dry. The term“substantially dry” is used herein to mean that the particles have aliquid content, typically water or other solution content, less thanabout 50%, preferably less than about 20%, more preferably less thanabout 10%, by weight of the particles. In general, the liquid content ofthe hydrogel-forming absorbent polymer particles is in the range of fromabout 0.01% to about 5% by weight of the particles. The individualparticles can be dried by any conventional method such as by heating.Alternatively, when the particles are formed using an aqueous reactionmixture, water can be removed from the reaction mixture by azeotropicdistillation. The polymer-containing aqueous reaction mixture can alsobe treated with a dewatering solvent such as methanol. Combinations ofthese drying procedures can also be used. The dewatered mass of polymercan then be chopped or pulverized to form substantially dry particles ofthe hydrogel-forming absorbent polymer.

Combination of High Capillary Suction Materials

Whilst materials as described in the above can satisfy the requirementsas such (e.g. a pure hydrogel forming material, or a pure foammaterial), preferred members for being used as storage absorbent membercomprise two or more of the materials. This allows often to utilizematerials which on their own do not satisfy the criteria, but thecombination does.

The principle function of such fluid storage members is to absorb thedischarged body fluid either directly or from other absorbent members(e.g., fluid acquisition/distribution members), and then retain suchfluid, even when subjected to pressures normally encountered as a resultof the wearer's movements.

Thus, high capillary suction absorbent members can be made bycombination of hydrogel forming materials with high surface areamaterials.

The amount of hydrogel-forming absorbent polymer contained in theabsorbent member may vary significantly. Furthermore, the concentrationof hydrogel may vary throughout a given member. In other words, a membermay have regions of relatively higher and relatively lower hydrogelconcentration.

In measuring the concentration of hydrogel-forming absorbent polymer ina given region of an absorbent member, the percent by weight of thehydrogel-forming polymer relative to the combined weight ofhydrogel-forming polymer and any other components (e.g., fibers,polymeric foams, etc.) that are present in the region containing thehydrogelling polymer is used. With this in mind, the concentration ofthe hydrogel-forming absorbent polymers in a given region of anabsorbent member of the present invention can be at least about 50%, atleast about 60%, at least about 70%, or at least about 80%, by totalweight of the absorbent member.

Notwithstanding the fact that regions of an absorbent member maycomprise relatively high concentrations of hydrogel-forming absorbentpolymer, where the high surface area material is fibrous in nature, theaggregate concentration of absorbent polymer in a given absorbent member(i.e., total weight of the hydrogel-forming absorbent polymer divided bythe total weight of the absorbent member×100%) will be up to about 75%by weight, preferably up to about 70% by weight, more preferably up toabout 65% by weight. Then, with these high surface area fiber-containingmembers, the concentration of the hydrogel-forming absorbent polymerwill be from about 10 to about 75% by weight, more typically from about15 to about 70% by weight, still more typically from about 20 to about65% by weight.

In those embodiments where the high surface area material is a polymericfoam, the absorbent members will preferably comprise at least about 1%by weight (on an aggregate basis), more preferably at least about 10% byweight, more preferably at least about 15% by weight, still morepreferably at least about 20% by weight, polymeric foam. Typically, suchstorage absorbent members will comprise from about 1 to about 98% byweight, more typically from about 10 to about 90% by weight, still moretypically from about 15 to about 85% by weight, and still more typicallyfrom about 20 to about 80% by weight, of the polymeric foam material. Asdiscussed above, these weight % ranges are based on the aggregateweights of the respective materials in an absorbent member; it isrecognized that regions of the absorbent member may contain greater andlesser amounts of the materials.

Of course, the relative levels of the absorbent polymer and high surfacearea material will be dictated by, for example, the absorptive capacityof the hydrogel-forming absorbent polymer, the specific high surfacearea material used, the nature of the high surface area material (e.g.,sheet or particle foam, particle size), etc. In this regard, althoughhigh levels of hydrogel-forming absorbent polymer provide absorbentmembers for making thin absorbent articles, to achieve the requisitelevel of capillary suction discussed above, there must be sufficienthigh surface area material to provide such suction capacity. Thus, whererelatively higher capillary suction foam is used, higher levels ofhydrogel-forming polymer may be employed. Conversely, where relativelylower capillary suction fibers are used, somewhat lower leves ofhydrogel-forming polymer will be employed. (Of course, where both highsurface area fibers and polymeric foams are employed, the level of totalhigh surface area material may vary, again depending on the relativeconcentration of each of these materials.) It is the difference incapillary sorption capacity between the polymeric foams and high surfacearea fibers described above that accounts for the different ranges ofhydrogel-forming polymer to be used in a given absorbent member.

As another example of a material that will provide integrity of themixture, in absorbent members comprising a blend of hydrogel-formingpolymer and high surface area fibers and/or particulate polymeric foam,the member can comprise a thermoplastic material. Upon melting, at leasta portion of this thermoplastic material migrates to the intersectionsof the respective member components, typically due to interparticle orinterfiber capillary gradients. These intersections become bond sitesfor the thermoplastic material. When cooled, the thermoplastic materialsat these intersections solidify to form the bond sites that hold thematrix of materials together.

Optional thermoplastic materials useful herein can be in any of avariety of forms including particulates, fibers, or combinations ofparticulates and fibers. Thermoplastic fibers are a particularlypreferred form because of their ability to form numerous bond sites.Suitable thermoplastic materials can be made from any thermoplasticpolymer that can be melted at temperatures that will not extensivelydamage the materials that comprise absorbent member. Preferably, themelting point of this thermoplastic material will be less than about190° C., and preferably between about 75° C. and about 175° C. In anyevent, the melting point of this thermoplastic material should be nolower than the temperature at which the thermally bonded absorbentstructures, when used in absorbent articles, are likely to be stored.The melting point of the thermoplastic material is typically no lowerthan about 50° C.

The thermoplastic materials, and in particular the thermoplastic fibers,can be made from a variety of thermoplastic polymers, includingpolyolefins such as polyethylene (e.g., PULPEX®) and polypropylene,polyesters, copolyesters, polyvinyl acetate, polyethylvinyl acetate,polyvinyl chloride, polyvinylidene chloride, polyacrylics, polyamides,copolyamides, polystyrenes, polyurethanes and copolymers of any of theforegoing such as vinyl chloride/vinyl acetate, and the like. Onepreferred thermoplastic binder fiber is PLEXAFIL® polyethylenemicrofibers (made by DuPont) that are also available as an about 20%blend with 80% cellulosic fibers sold under the tradename KITTYHAWK®(made by Weyerhaeuser Co.) Depending upon the desired characteristicsfor the resulting thermally bonded absorbent member, suitablethermoplastic materials include hydrophobic fibers that have been madehydrophilic, such as surfactant-treated or silica-treated thermoplasticfibers derived from, for example, polyolefins such as polyethylene orpolypropylene, polyacrylics, polyamides, polystyrenes, polyurethanes andthe like. The surface of the hydrophobic thermoplastic fiber can berendered hydrophilic by treatment with a surfactant, such as a nonionicor anionic surfactant, e.g., by spraying the fiber with a surfactant, bydipping the fiber into a surfactant or by including the surfactant aspart of the polymer melt in producing the thermoplastic fiber. Uponmelting and resolidification, the surfactant will tend to remain at thesurfaces of the thermoplastic fiber. Suitable surfactants includenonionic surfactants such as Brij® 76 manufactured by ICI Americas, Inc.of Wilmington, Del., and various surfactants sold under the Pegosperse®trademark by Glyco Chemical, Inc. of Greenwich, Conn. Besides nonionicsurfactants, anionic surfactants can also be used. These surfactants canbe applied to the thermoplastic fibers at levels of, for example, fromabout 0.2 to about 1 g. per sq. of centimeter of thermoplastic fiber.

Suitable thermoplastic fibers can be made from a single polymer(monocomponent fibers), or can be made from more than one polymer (e.g.,bicomponent fibers). As used herein, “bicomponent fibers” refers tothermoplastic fibers that comprise a core fiber made from one polymerthat is encased within a thermoplastic sheath made from a differentpolymer. The polymer comprising the sheath often melts at a different,typically lower, temperature than the polymer comprising the core. As aresult, these bicomponent fibers provide thermal bonding due to meltingof the sheath polymer, while retaining the desirable strengthcharacteristics of the core polymer.

Suitable bicomponent fibers for use in the present invention can includesheath/core fibers having the following polymer combinations:polyethylene/polypropylene, polyethylvinyl acetate/polypropylene,polyethylene/polyester, polypropylene/polyester, copolyester/polyester,and the like. Particularly suitable bicomponent thermoplastic fibers foruse herein are those having a polypropylene or polyester core, and alower melting copolyester, polyethylvinyl acetate or polyethylene sheath(e.g., DANAKLON®, CELBOND® or CHISSO® bicomponent fibers). Thesebicomponent fibers can be concentric or eccentric. As used herein, theterms “concentric” and “eccentric” refer to whether the sheath has athickness that is even, or uneven, through the cross-sectional area ofthe bicomponent fiber. Eccentric bicomponent fibers can be desirable inproviding more compressive strength at lower fiber thicknesses. Suitablebicomponent fibers for use herein can be either uncrimped (i.e. unbent)or crimped (i.e. bent). Bicomponent fibers can be crimped by typicaltextile means such as, for example, a stuffer box method or the gearcrimp method to achieve a predominantly two-dimensional or “flat” crimp.

In the case of thermoplastic fibers, their length can vary dependingupon the particular melt point and other properties desired for thesefibers. Typically, these thermoplastic fibers have a length from about0.3 to about 7.5 cm long, preferably from about 0.4 to about 3.0 cmlong, and most preferably from about 0.6 to about 1.2 cm long. Theproperties, including melt point, of these thermoplastic fibers can alsobe adjusted by varying the diameter (caliper) of the fibers. Thediameter of these thermoplastic fibers is typically defined in terms ofeither denier (grams per 9000 meters) or decitex (grams per 10,000meters). Suitable bicomponent thermoplastic fibers can have a decitex inthe range from about 1.0 to about 20, preferably from about 1.4 to about10, and most preferably from about 1.7 to about 3.3.

The compressive modulus of these thermoplastic materials, and especiallythat of the thermoplastic fibers, can also be important. The compressivemodulus of thermoplastic fibers is affected not only by their length anddiameter, but also by the composition and properties of the polymer orpolymers from which they are made, the shape and configuration of thefibers (e.g., concentric or eccentric, crimped or uncrimped), and likefactors. Differences in the compressive modulus of these thermoplasticfibers can be used to alter the properties, and especially the densitycharacteristics, of the respective absorbent members during preparationof the absorbent core.

Other Fluid Handling Member Components and Materials

Storage absorbent members according to the present invention can includeother optional components that can be present in absorbent webs. Forexample, a reinforcing scrim can be positioned within the storageabsorbent member, or between the respective absorbent members of theabsorbent core. Such reinforcing scrims should be of such configurationas to not form interfacial barriers to liquid transfer, especially ifpositioned between the respective absorbent members of the absorbentcore. In addition, several binders may be used to provide dry and wetintegrity to the absorbent core and/or the absorbent storage memberitself. In particular, hydrophilic glue fibers may be used to providebonds between the high surface area materials and the other absorbentsuch as osmotic absorbent material. This is in particular critical forparticulate high surface area materials. It is preferred that the amountof binder used is as low as possible, so as not to impair the capillarysorption properties of the absorbent member. However, the skilledartisan will recognize that there are also binders that may enhance thecapillary sorption properties of the absorbent member such as fiberizedhydrophilic glue with sufficiently high surface area. In this case, thehigh surface area hydrophilic glue may provide both the liquid handlingfunction and the integrity function, in one material. Also, therespective absorbent member, or the entire absorbent core, can beenveloped within a liquid pervious sheet, such as a tissue paper sheet,to obviate user concern regarding loose particulate absorbent polymer,as long as the capillary continuity is not disturbed.

Other optional components that can be included are materials to controlodor, contain fecal matter, etc. Also, any absorbent member comprisingparticulate osmotic absorbent or high surface area material, or theentire absorbent core, can be enveloped within a liquid pervious sheet,such as a tissue paper sheet, to obviate user concern regarding looseparticulate absorbent polymer.

When integrity is introduced via a binder material, suitable binders aremelt-blown adhesives such as those described in U.S. Pat. No. 5,560,878,issued Oct. 1, 1996 to Dragoo et al., the disclosure of which isincorporated herein by reference. Processes for combining melt-blownadhesives with the requisite hydrogel-forming polymer and high surfacearea material is also described in detail in the '878 patent.

EXAMPLES Samples 1, 2, 3-HIPEs as Distribution Material

The following Samples A.5 to A.7 are of the polymeric foam type, and areprepared as described generally in the Examples section of U.S. Pat. No.5,563,179, supra. Generally, this process comprises appropriate mixingof an aqueous phase containing selected salts with an oil phasecontaining selected monomers and emulsifiers. The aqueous phasetypically contains an initiator such as potassium persulfate andinorganic salt such as calcium chloride. The oil phase typicallycontains a blend of monomers such as 2-ethylhexylacrylate andcrosslinking monomers such as divinyl benzene (which contains ethylstyrene as an impurity) and 1,6-hexanedioldiacrylate. Adjuvants such asantioxidants, opacifying agents, pigments, dyes, fillers, and othergenerally unreactive chemicals, can also be added to either phase.

The separate streams of the oil phase and water phase (typically heatedto between about 30° and about 90° C.) are fed to a dynamic mixingapparatus. Thorough mixing of the combined streams in the dynamic mixingapparatus is achieved by means of a pin impeller. The ratio of theaqueous phase and the oil phase, referred to as the “water-to-oilratio”, or W:O, is used to control the density of the ultimate foamproduced. A detailed description of the apparatus and the procedures forestablishing the initial HIPE formation is described in more detail inthe Examples section of U.S. Pat. No. 5,563,179, supra.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at a specified RPM. The flow rate ofthe water phase is then steadily increased to a rate of 44.1 cm³/sec ina time period of about 30 sec. and the oil phase flow rate is reduced to1.25 g/sec over a time period of about 1 min. The back pressure createdby the dynamic and static mixers at this point is typically betweenabout 3 and about 8 PSI (about 21 to about 55 kPa). The impeller speedis then adjusted to the desired RPM over a period of 120 sec. The systemback pressure responds to this adjustment and remains constantthereafter.

The HIPE from the static mixer is collected in a round polypropylenetub, 17 in. (43 cm) in. diameter and 7.5 in. (10 cm) high, with aconcentric insert made of Celcon plastic. The insert is 5.0 in. (12.7cm) in diameter at its base and 4.75 in. (12 cm) in diameter at its topand is 6.75 in. (17.1 cm) high. The HIPE-containing tubs are kept in aroom maintained at 65° C. for 18 hours to cure and provide a polymericHIPE foam.

The cured HIPE foam is removed from the tubs. The foam at this pointcontains residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator). The foam is sliced witha sharp reciprocating saw blade into sheets of desired thickness. Thesesheets are then subjected to compression in a series of 2 porous niprolls equipped with vacuum which gradually reduces the residual waterphase content of the foam to about 2 times (2×) the weight of thepolymerized monomers. At this point, the sheets are then resaturatedwith a 4% CaCl₂ solution at 60° C., are squeezed in a series of 3 porousnip rolls equipped with vacuum to a water phase content of about 2×. TheCaCl₂ content of the foam is between 2 and 10%.

The HIPE foam is then dried in air for about 16 hours or thermally driedcontinuously. Such drying reduces the moisture content to about 4-20% byweight of polymerized material.

Sample 1

Anhydrous calcium chloride (36.32 kg) and potassium persulfate (189 g)are dissolved in 378 liters of water. This provides the water phasestream to be used in a continuous process for forming a HIPE emulsion.

To a monomer combination comprising distilled divinylbenzene (39%divinylbenzene and 61% ethyl styrene) (2640 g), 2-ethylhexyl acrylate(4720 g), and hexanedioldiacrylate (640 g) is added a diglycerolmonooleate emulsifier (480 g), ditallow dimethyl ammonium methyl suflate(80 g), and Tinuvin 765 (20 g). The diglycerol monooleate emulsifier(Grindsted Products; Brabrand, Denmark) comprises approximately 81%diglycerol monooleate, 1% other diglycerol monoesters, 3% polyols, and15% other polyglycerol esters, imparts a minimum oil/water interfacialtension value of approximately 2.7 dyne/cm and has an oil/water criticalaggregation concentration of approximately 2.8 wt %. After mixing, thiscombination of materials is allowed to settle overnight. No visibleresidue is formed and all of the mixture is withdrawn and used as theoil phase in a continuous process for forming a HIPE emulsion.

Separate streams of the oil phase (25° C.) and water phase (53°-55° C.)are fed to a dynamic mixing apparatus. Thorough mixing of the combinedstreams in the dynamic mixing apparatus is achieved by means of a pinimpeller. The pin impeller comprises a cylindrical shaft of about 36.5cm in length with a diameter of about 2.9 cm. The shaft holds 6 rows ofpins, 3 rows having 33 pins and 3 rows having 34 pins, each of the threepins at each level disposed at an angle of 120° to each other, with thenext level down disposed at 60° to its neighboring level with each levelseparated by 0.03 mm, each pin having a diameter of 0.5 cm extendingoutwardly from the central axis of the shaft to a length of 2.3 cm. Thepin impeller is mounted in a cylindrical sleeve which forms the dynamicmixing apparatus, and the pins have a clearance of 1.5 mm from the wallsof the cylindrical sleeve.

A minor portion of the effluent exiting the dynamic mixing apparatus iswithdrawn and enters a recirculation zone, as shown in the Figure inco-pending U.S. patent application Ser. No. 08/716,510 (T. A.DesMarais), filed Sep. 17, 1996 (herein incorporated by reference). TheWaukesha pump in the recirculation zone returns the minor portion to theentry point of the oil and water phase flow streams to the dynamicmixing zone.

A spiral static mixer is mounted downstream from the dynamic mixingapparatus to provide back pressure in the dynamic mixing apparatus andto provide improved incorporation of components into the HIPE that iseventually formed. The static mixer (TAH Industries Model 100-812) has12 elements with a 1 inch (2.5 cm) outside diameter. A hose is mounteddownstream from the static mixer to facilitate delivery of the emulsionto the device used for curing. Optionally an additional static mixer isused to provide addition back pressure to keep the hose filled. Theoptional static mixer can be a 1 inch (2.5 cm) pipe, 12 element mixer(McMaster-Carr Model 3529K53).

The combined mixing and recirculation apparatus set-up is filled withoil phase and water phase at a ratio of 4 parts water to 1 part oil. Thedynamic mixing apparatus is vented to allow air to escape while fillingthe apparatus completely. The flow rates during filling are 7.57 g/secoil phase and 30.3 cm³/sec water phase.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at 850 RPM and recirculation is begunat a rate of about 30 cm³/sec. The flow rate of the water phase is thensteadily increased to a rate of 151.3 cm³/sec over a time period ofabout 1 min., and the oil phase flow rate is reduced to 2.52 g/sec overa time period of about 3 min. The recirculation rate is steadilyincreased to about 150 cm³/sec during the latter time period. The backpressure created by the dynamic zone and static mixers at this point isabout 4.9 PSI (33.8 kPa), which represents the total pressure drop ofthe system. The Waukesha pump speed is then steadily decreased to ayield a recirculation rate of about 75 cm³/sec.

The HIPE flowing from the static mixer at this point is collected in around polyethylene tub, 40 in. (102 cm) in diameter and 12.5 in (31.8cm) high, with removable sides, much like a springform pan used incooking cakes. A pipe-like polyethylene insert 12.5 in (31.8 cm) indiameter at its base is firmly affixed to the center of the base and is12.5 in (31.8 cm) high. The HIPE-containing tubs are kept in a roommaintained at 65° C. for 18 hours to bring about polymerization and formthe foam.

The cured HIPE foam is removed from the curing tubs. The foam at thispoint has residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator) about 55-65 times(55-65×) the weight of polymerized monomers. The foam is sliced with asharp reciprocating saw blade into sheets which are 0.2 inches (5.1 mm)in thickness. These sheets are then subjected to compression in a seriesof 2 porous nip rolls equipped with vacuum which gradually reduce theresidual water phase content of the foam to about 3 times (3×) theweight of the polymerized material. At this point, the sheets are thenresaturated with a 4% CaCl₂ solution at 60° C., are squeezed in a seriesof 3 porous nip rolls equipped with vacuum to a water phase content ofabout 1.5-2×. The CaCl₂ content of the foam is between 6 and 10%.

The foam remains compressed after the final nip at a thickness of about0.027 in. (0.069 cm). The foam is then dried in air for about 16 hours.Such drying reduces the moisture content to about 9-17% by weight ofpolymerized material. At this point, the foam sheets are very drapeable.

Sample 2

Anhydrous calcium chloride (36.32 kg) and potassium persulfate (189 g)are dissolved in 378 liters of water. This provides the water phasestream to be used in a continuous process for forming a HIPE emulsion.

To a monomer combination comprising distilled divinylbenzene (42.4%divinylbenzene and 57.6% ethyl styrene) (2640 g), 2-ethylhexyl acrylate(4400 g), and hexanedioldiacrylate (960 g) is added a diglycerolmonooleate emulsifier (640 g), ditallow dimethyl ammonium methyl suflate(80 g), and Tinuvin 765 (20 g). The diglycerol monooleate emulsifier(Grindsted Products; Brabrand, Denmark) comprises approximately 81%diglycerol monooleate, 1% other diglycerol monoesters, 3% polyols, and15% other polyglycerol esters, imparts a minimum oil/water interfacialtension value of approximately 2.7 dyne/cm and has an oil/water criticalaggregation concentration of approximately 2.8 wt %. After mixing, thiscombination of materials is allowed to settle overnight. No visibleresidue is formed and all of the mixture is withdrawn and used as theoil phase in a continuous process for forming a HIPE emulsion.

Separate streams of the oil phase (25° C.) and water phase (75°-77° C.)are fed to a dynamic mixing apparatus. Thorough mixing of the combinedstreams in the dynamic mixing apparatus is achieved by means of a pinimpeller. The pin impeller comprises a cylindrical shaft of about 36.5cm in length with a diameter of about 2.9 cm. The shaft holds 6 rows ofpins, 3 rows having 33 pins and 3 rows having 34 pins, each of the threepins at each level disposed at an angle of 120° to each other, with thenext level down disposed at 60° to its neighboring level with each levelseparated by 0.03 mm, each pin having a diameter of 0.5 cm extendingoutwardly from the central axis of the shaft to a length of 2.3 cm. Thepin impeller is mounted in a cylindrical sleeve which forms the dynamicmixing apparatus, and the pins have a clearance of 1.5 mm from the wallsof the cylindrical sleeve.

A minor portion of the effluent exiting the dynamic mixing apparatus iswithdrawn and enters a recirculation zone, as shown in the Figure inco-pending U.S. patent application Ser. No. 08/716,510 (T. A.DesMarais), filed Sep. 17, 1996 (herein incorporated by reference). TheWaukesha pump in the recirculation zone returns the minor portion to theentry point of the oil and water phase flow streams to the dynamicmixing zone.

A spiral static mixer is mounted downstream from the dynamic mixingapparatus to provide back pressure in the dynamic mixing apparatus andto provide improved incorporation of components into the HIPE that iseventually formed. The static mixer (TAH Industries Model 101-212)normally has 12 elements with a 1.5 inch (3.8 cm) outside diameter, but7 inches (17.8 cm) were removed to fit in the equipment space. A hose ismounted downstream from the static mixer to facilitate delivery of theemulsion to the device used for curing. Optionally an additional staticmixer is used to provide addition back pressure to keep the hose filled.The optional static mixer can be the same as the first withoutmodification.

The combined mixing and recirculation apparatus set-up is filled withoil phase and water phase at a ratio of 4 parts water to 1 part oil. Thedynamic mixing apparatus is vented to allow air to escape while fillingthe apparatus completely. The flow rates during filling are 7.57 g/secoil phase and 30.3 cm³/sec water phase.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at 800 RPM and recirculation is begunat a rate of about 30 cm³/sec. The flow rate of the water phase is thensteadily increased to a rate of 151.3 cm³/sec over a time period ofabout 1 min., and the oil phase flow rate is reduced to 2.52 g/sec overa time period of about 3 min. The recirculation rate is steadilyincreased to about 150 cm³/sec during the latter time period. The backpressure created by the dynamic zone and static mixers at this point isabout 4.2 PSI (29 kPa), which represents the total pressure drop of thesystem.

The HIPE flowing from the static mixer at this point is collected in around polyethylene tub, 40 in. (102 cm) in diameter and 12.5 in (31.8cm) high, with removable sides, much like a springform pan used incooking cakes. A pipe-like polyethylene insert 12.5 in (31.8 cm) indiameter at its base is firmly affixed to the center of the base and is12.5 in (31.8 cm) high. The HIPE-containing tubs are kept in a roommaintained at 65° C. for 18 hours to bring about polymerization and formthe foam.

The cured HIPE foam is removed from the curing tubs. The foam at thispoint has residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator) about 58-62 times(58-62×) the weight of polymerized monomers. The foam is sliced with asharp reciprocating saw blade into sheets which are 0.2 inches (5.1 mm)in thickness. These sheets are then subjected to compression in a seriesof 2 porous nip rolls equipped with vacuum which gradually reduce theresidual water phase content of the foam to about 6 times (6×) theweight of the polymerized material. At this point, the sheets are thenresaturated with a 1.5% CaCl₂ solution at 60° C., are squeezed in aseries of 3 porous nip rolls equipped with vacuum to a water phasecontent of about 2×. The CaCl₂ content of the foam is between 3 and 6%.

The foam remains compressed after the final nip at a thickness of about0.047 in. (0.071 cm). The foam is then dried in air for about 16 hours.Such drying reduces the moisture content to about 9-17% by weight ofpolymerized material. At this point, the foam sheets are very drapeable.

Sample 3

Anhydrous calcium chloride (36.32 kg) and potassium persulfate (189 g)are dissolved in 378 liters of water. This provides the water phasestream to be used in a continuous process for forming a HIPE emulsion.

To a monomer combination comprising distilled divinylbenzene (42.4%divinylbenzene and 57.6% ethyl styrene) (2640 g), 2-ethylhexyl acrylate(4400 g), and hexanedioldiacrylate (960 g) is added a diglycerolmonooleate emulsifier (640 g), ditallow dimethyl ammonium methyl suflate(80 g), and Tinuvin 765 (40 g). The diglycerol monooleate emulsifier(Grindsted Products; Brabrand, Denmark) comprises approximately 81%diglycerol monooleate, 1% other diglycerol monoesters, 3% polyols, and15% other polyglycerol esters, imparts a minimum oil/water interfacialtension value of approximately 2.7 dyne/cm and has an oil/water criticalaggregation concentration of approximately 2.8 wt %. After mixing, thiscombination of materials is allowed to settle overnight. No visibleresidue is formed and all of the mixture is withdrawn and used as theoil phase in a continuous process for forming a HIPE emulsion.

Separate streams of the oil phase (25° C.) and water phase (75°-77° C.)are fed to a dynamic mixing apparatus. Thorough mixing of the combinedstreams in the dynamic mixing apparatus is achieved by means of a pinimpeller. The pin impeller comprises a cylindrical shaft of about 21.6cm in length with a diameter of about 1.9 cm. The shaft holds 6 rows ofpins, one level with 3 rows having 21 pins and another level with 3 rowshaving 21 pins, each of the three pins at each level disposed at anangle of 120° to each other, with the next level down disposed at 60° toits neighboring level with each level separated by 0.03 mm, each havinga diameter of 0.5 cm extending outwardly from the central axis of theshaft to a length of 1.4 cm. The pin impeller is mounted in acylindrical sleeve which forms the dynamic mixing apparatus, and thepins have a clearance of 3 mm from the walls of the cylindrical sleeve.

A minor portion of the effluent exiting the dynamic mixing apparatus iswithdrawn and enters a recirculation zone, as shown in the Figure inco-pending U.S. patent application Ser. No. 08/716,510 (T. A.DesMarais), filed Sep. 17, 1996 (herein incorporated by reference). TheWaukesha pump in the recirculation zone returns the minor portion to theentry point of the oil and water phase flow streams to the dynamicmixing zone.

A spiral static mixer is mounted downstream from the dynamic mixingapparatus to provide back pressure in the dynamic mixing apparatus andto provide improved incorporation of components into the HIPE that iseventually formed. The static mixer (TAH Industries Model 070-821),modified by cutting off 2.4 inches (6.1 cm) of its original length) is14 inches (35.6 cm) long with a 0.5 inch (1.3 cm) outside diameter.

The combined mixing and recirculation apparatus set-up is filled withoil phase and water phase at a ratio of 4 parts water to 1 part oil. Thedynamic mixing apparatus is vented to allow air to escape while fillingthe apparatus completely. The flow rates during filling are 1.89 g/secoil phase and 7.56 cm³/sec water phase.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at 1000 RPM and recirculation is begunat a rate of about 8 cm³/sec. The flow rate of the water phase is thensteadily increased to a rate of 45.4 cm³/sec over a time period of about1 min., and the oil phase flow rate is reduced to 0.6 g/sec over a timeperiod of about 3 min. The recirculation rate is steadily increased toabout 45 cm³/sec during the latter time period. The back pressurecreated by the dynamic zone and static mixers at this point is about 2.9PSI (20 kPa), which represents the total pressure drop of the system.

The HIPE flowing from the static mixer at this point is collected in around polypropylene tub, 17 in. (43 cm) in diameter and 7.5 in (10 cm)high, with a concentric insert made of Celcon plastic. The insert is 5in (12.7 cm) in diameter at its base and 4.75 in (12 cm) in diameter atits top and is 6.75 in (17.1 cm) high. The HIPE-containing tubs are keptin a room maintained at 65° C. for 18 hours to bring aboutpolymerization and form the foam.

The cured HIPE foam is removed from the curing tubs. The foam at thispoint has residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator) about 70-80 times(70-80×) the weight of polymerized monomers. The foam is sliced with asharp reciprocating saw blade into sheets which are 0.185 inches (4.7mm) in thickness. These sheets are then subjected to compression in aseries of 2 porous nip rolls equipped with vacuum which gradually reducethe residual water phase content of the foam to about 3 times (3×) theweight of the polymerized material. At this point, the sheets are thenresaturated with a 1.5% CaCl₂ solution at 60° C., are squeezed in aseries of 3 porous nip rolls equipped with vacuum to a water phasecontent of about 2×. The CaCl₂ content of the foam is between 3 and 5%.

The foam remains compressed after the final nip at a thickness of about0.031 in. (0.079 cm). The foam is then dried in air for about 16 hours.Such drying reduces the moisture content to about 9-17% by weight ofpolymerized material. At this point, the foam sheets are very drapeable.

High Capillary Suction Storage Member (Samples S . . . ) Sample S.1Storage Absorbent Member Comprising Glass Microfibers

This example describes a high capillary suction absorbent membercomprising hydrogel-forming absorbent polymer and high surface areaglass micro fibers as formed using a wet end forming process forincreased density and structural organization over conventional airdeposition processes. In order to construct such a hydrogel-formingabsorbent polymer containing member which approaches a homogeneousdistribution of absorbent polymer in the glass micro fiber matrix, thefollowing procedure is followed.

A mixture of 4.0 gms of ASAP 2300 (available from Chemdal LTD, asubsidiary of American Colloid Co., Arlington Heights, Ill.; alsoavailable from The Procter & Gamble Co., Paper Technology Division,Cincinnati, Ohio) and 4.0 gms of glass micro fiber (available as“Q-FIBERS, Code 108, 110 Bulk” from Manville Sales Corp., Denver, Colo.)are combined in an explosion resistant 3-gallon Commercial grade Warnerblender with approximately 500 ml of 3A alcohol (95% ethanol, 5%methanol), or Isopropanol, or similar liquids which will not degrade norabsorb into the structure or composition of the involved polymers. Themixture is stirred on low speed for approximately 5 min. The mixture ispoured into a 6 in.×6 in. “Paper Formation Box” with an 80 mesh NylonForming Wire (available from Appleton Mfg. Div., Productive Solutions,Inc., Neenah, Wis.) at the bottom of the upper portion of the FormationBox. Liquid level is brought to about 8 in (about 20.3 cm) above thescreen with addition of 3A alcohol, or appropriate solution. A paddle isused to mix the solution thoroughly in the top of the Formation boxbefore liquid evacuation. A valve is opened below the forming wire andliquid is drained rapidly to ensure a uniform deposition on the formingwire. The screen is removed from the “Formation box”, pulled across avacuum source for removal of loosely held liquid, and allowed to air dryovernight in a desiccator containing a desiccant (such as DRIERITE,Sigme Chem. Co., St. Louis, Mo. 63178) to ensure uniform moisturecontent. Once dry, the absorbent member is removed from the formingscreen. A 5.4 cm cylindrical-shaped structure is arch-punched from themember for measurement of capillary sorption absorbent capacity.

Sample S.2 Preparation of High Surface Area Foam from a HIPE

Anhydrous calcium chloride (36.32 kg) and potassium persulfate (189 g)are dissolved in 378 liters of water. This provides the water phasestream to be used in a continuous process for forming a HIPE emulsion.

To a monomer combination comprising distilled divinylbenzene (42.4%divinylbenzene and 57.6% ethyl styrene) (2640 g), 2-ethylhexyl acrylate(4400 g), and hexanedioldiacrylate (960 g) is added a diglycerolmonooleate emulsifier (480 g), ditallow dimethyl ammonium methyl sulfate(80 g), and Tinuvin 765 (20 g). The diglycerol monooleate emulsifier(Grindsted Products; Brabrand, Denmark) comprises approximately 81%diglycerol monooleate, 1% other diglycerol monoesters, 3% polyols, and15% other polyglycerol esters, imparts a minimum oil/water interfacialtension value of approximately 2.7 dyne/cm and has an oil/water criticalaggregation concentration of approximately 2.8 wt %. After mixing, thiscombination of materials is allowed to settle overnight. No visibleresidue is formed and all of the mixture is withdrawn and used as theoil phase in a continuous process for forming a HIPE emulsion.

Separate streams of the oil phase (25° C.) and water phase (53°-55° C.)are fed to a dynamic mixing apparatus. Thorough mixing of the combinedstreams in the dynamic mixing apparatus is achieved by means of a pinimpeller. The pin impeller comprises a cylindrical shaft of about 36.5cm in length with a diameter of about 2.9 cm. The shaft holds 6 rows ofpins, 3 rows having 33 pins and 3 rows having 34 pins, each of the threepins at each level disposed at an angle of 120° to each other, with thenext level down disposed at 60° to its neighboring level with each levelseparated by 0.03 mm, each having a diameter of 0.5 cm extendingoutwardly from the central axis of the shaft to a length of 2.3 cm. Thepin impeller is mounted in a cylindrical sleeve which forms the dynamicmixing apparatus, and the pins have a clearance of 1.5 mm from the wallsof the cylindrical sleeve.

A minor portion of the effluent exiting the dynamic mixing apparatus iswithdrawn and enters a recirculation zone, as shown in the Figure ofco-pending U.S. patent application Ser. No. 08/716,510, filed Sep. 17,1996 by DesMarais, the disclosure of which is incorporated by referenceherein. The Waukesha pump in the recirculation zone returns the minorportion to the entry point of the oil and water phase flow streams tothe dynamic mixing zone.

The static mixer (TAH Industries Model 100-812) has 12 elements with a 1in. (2.5 cm) outside diameter. A hose is mounted downstream from thestatic mixer to facilitate delivery of the emulsion to the device usedfor curing. Optionally an additional static mixer is used to provideaddition back pressure to keep the hose filled. The optional staticmixer can be a 1 in. (2.5 cm) pipe, 12 element mixer (McMaster-Carr,Aurora, Ohio, Model 3529K53).

The combined mixing and recirculation apparatus set-up is filled withoil phase and water phase at a ratio of 4 parts water to 1 part oil. Thedynamic mixing apparatus is vented to allow air to escape while fillingthe apparatus completely. The flow rates during filling are 7.57 g/secoil phase and 30.3 cm³/sec water phase.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at 1750 RPM and recirculation is begunat a rate of about 30 cm³/sec. The flow rate of the water phase is thensteadily increased to a rate of 151.3 cm³/sec over a time period ofabout 1 min., and the oil phase flow rate is reduced to 3.03 g/sec overa time period of about 3 min. The recirculation rate is steadilyincreased to about 150 cm³/sec during the latter time period. The backpressure created by the dynamic zone and static mixers at this point isabout 19.9 PSI (137 kPa), which represents the total pressure drop ofthe system. The Waukesha pump (Model 30) speed is then steadilydecreased to a yield a recirculation rate of about 75 cm³/sec.

The HIPE flowing from the static mixer at this point is collected in around polyethylene tub, 40 in. (102 cm) in diameter and 12.5 in. (31.8cm) high, with removable sides, much like a springform pan used incooking cakes. A pipe-like polyethylene insert 12.5 in. (31.8 cm) indiameter at its base is firmly affixed to the center of the base and is12.5 in. (31.8 cm) high. The HIPE-containing tubs are kept in a roommaintained at 65° C. for 18 hours to effect polymerization and form thefoam.

The cured HIPE foam is removed from the curing tubs. The foam at thispoint has residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator) about 48-52 times(48-52×) the weight of polymerized monomers. The foam is sliced with asharp reciprocating saw blade into sheets which are 0.185 inches (4.7mm) in thickness. These sheets are then subjected to compression in aseries of 2 porous nip rolls equipped with vacuum which gradually reducethe residual water phase content of the foam to about 6 times (6×) theweight of the polymerized material. At this point, the sheets are thenresaturated with a 1.5% CaCl₂ solution at 60° C., are squeezed in aseries of 3 porous nip rolls equipped with vacuum to a water phasecontent of about 4×. The CaCl₂ content of the foam is between 8 and 10%.

The foam remains compressed after the final nip at a thickness of about0.021 in. (0.053 cm). The foam is then dried in air for about 16 hours.Such drying reduces the moisture content to about 9-17% by weight ofpolymerized material. At this point, the foam sheets are very drapeableand “thin-after-drying”.

Sample S.3 Preparation of High Surface Area Foam from a HIPE

The water and oil phase streams to be used in a continuous process forforming a HIPE emulsion is prepared according to Sample S.2. Separatestreams of the oil phase (25° C.) and water phase (53°-55° C.) are fedto a dynamic mixing apparatus as detailed in Sample S.2.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at 1700 RPM and recirculation is begunat a rate of about 30 cm³/sec. The flow rate of the water phase is thensteadily increased to a rate of 151.3 cm³/sec over a time period ofabout 1 min., and the oil phase flow rate is reduced to 3.36 g/sec overa time period of about 3 min. The recirculation rate is steadilyincreased to about 150 cm³/sec during the latter time period. The backpressure created by the dynamic zone and static mixers at this point isabout 19.7 PSI (136 kPa), which represents the total pressure drop ofthe system. The Waukesha pump speed is then steadily decreased to ayield a recirculation rate of about 75 cm³/sec.

The HIPE flowing from the static mixer at this point is collected andcured into a polymeric foam as detailed in Sample S.2.

The cured HIPE foam is removed from the curing tubs. The foam at thispoint has residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator) about 43-47 times(43-47×) the weight of polymerized monomers. The foam is sliced with asharp reciprocating saw blade into sheets which are 0.185 inches (4.7mm) in thickness. These sheets are then subjected to compression in aseries of 2 porous nip rolls equipped with vacuum which gradually reducethe residual water phase content of the foam to about 6 times (6×) theweight of the polymerized material. At this point, the sheets are thenresaturated with a 1.5% CaCl₂ solution at 60° C., are squeezed in aseries of 3 porous nip rolls equipped with vacuum to a water phasecontent of about 4×. The CaCl₂ content of the foam is between 8 and 10%.

The foam remains compressed after the final nip at a thickness of about0.028 in. (0.071 cm). The foam is then dried in air for about 16 hours.Such drying reduces the moisture content to about 9-17% by weight ofpolymerized material. At this point, the foam sheets are very drapeableand “thin-after-drying”.

Sample S.4 Preparation of High Surface Area Foam from a HIPE

The water and oil phase streams to be used in a continuous process forforming a HIPE emulsion is prepared according to Sample S.2. Separatestreams of the oil phase (25° C.) and water phase (53°-55° C.) are fedto a dynamic mixing apparatus as detailed in Sample S.2.

Once the apparatus set-up is filled, agitation is begun in the dynamicmixer, with the impeller turning at 1750 RPM and recirculation is begunat a rate of about 30 cm³/sec. The flow rate of the water phase is thensteadily increased to a rate of 151.3 cm³/sec over a time period ofabout 1 min., and the oil phase flow rate is reduced to 3.78 g/sec overa time period of about 3 min. The recirculation rate is steadilyincreased to about 150 cm³/sec during the latter time period. The backpressure created by the dynamic zone and static mixers at this point isabout 18.7 PSI (129 kPa), which represents the total pressure drop ofthe system. The Waukesha pump speed is then steadily decreased to ayield a recirculation rate of about 75 cm³/sec.

The HIPE flowing from the static mixer at this point is collected andcured into a polymeric foam as detailed in Sample S.2.

The cured HIPE foam is removed from the curing tubs. The foam at thispoint has residual water phase (containing dissolved emulsifiers,electrolyte, initiator residues, and initiator) about 38-42 times(38-42×) the weight of polymerized monomers. The foam is sliced with asharp reciprocating saw blade into sheets which are 0.185 inches (4.7mm) in thickness. These sheets are then subjected to compression in aseries of 2 porous nip rolls equipped with vacuum which gradually reducethe residual water phase content of the foam to about 6 times (6×) theweight of the polymerized material. At this point, the sheets are thenresaturated with a 1.5% CaCl₂ solution at 60° C., are squeezed in aseries of 3 porous nip rolls equipped with vacuum to a water phasecontent of about 4×. The CaCl₂ content of the foam is between 8 and 10%.

The foam remains compressed after the final nip at a thickness of about0.028 in. (0.071 cm). The foam is then dried in air for about 16 hours.Such drying reduces the moisture content to about 9-17% by weight ofpolymerized material. At this point, the foam sheets are very drapeableand “thin-after-drying”.

Sample S.5 Storage Absorbent Member Comprising High Surface AreaPolymeric Foam Material

This example describes a high capillary suction absorbent membercomprising hydrogel-forming absorbent polymer and the high suctionpolymeric foam material prepared according to Sample S.3. In order toconstruct a hydrogel-forming absorbent polymer containing member whichapproaches a relatively homogeneous distribution of absorbent polymerand polymeric foam, the following procedure is followed.

10 g of air dried polymeric foam (prepared according to Sample S.3above) is placed in a blender (Osterizer model 848-36L) equipped with a1.25 liter jar, into which 1 liter of 2% calcium chloride solution hasbeen placed. After ensuring that all of the foam material is submerged,the blender is agitated on the ‘Liquify’ (high setting) for 10 secondsand then additionally agitated on the ‘Grate’ setting for 5 sec. Theresultant slurry is then transferred to a Buchner funnel (Coors USAmodel 60283) lined with a paper towel. Approximately 500 ml of fluid isfreely drained from the sample. The sample is then covered with a rubbermembrane and vacuum is applied (approximately 500 mm Hg or about 66 kPa)to dewater the sample to a weight of 50 to 60 grams.

The sample is returned to a dry blender jar and dispersed with theagitation set on ‘Liquify’ while the jar and base are inverted andreturned to upright several times to disperse the sample toapproximately individual particles. The dispersed sample is then airdried under ambient conditions and then the foam particles are combinedwith hydrogel-forming absorbent polymer (ASAP 2300, available fromChemdal Corporation of Palantine, Ill. also available from The Procter &Gamble Co., Paper Technology Division, Cincinnati, Ohio), to provide astorage absorbent member consisting of a homogeneous blend of 50%, byweight, hydrogel forming polymer and 50%, by weight, high surface areapolymeric foam.

Sample S.6 Storage Absorbent Member Comprising High Surface Area Fibrets

This example describes a high capillary suction absorbent membercomprising hydrogel-forming absorbent polymer and high surface areafibrets. High surface area fibrets, available from Hoechst CelaneseCorp. (Charlotte, N.C.) as cellulose acetate Fibrets®, are combined withhydrogel-forming absorbent polymer (ASAP 2300, available from ChemdalCorporation of Palantine, Ill.; also available from The Procter & GambleCo., Paper Technology Division, Cincinnati, Ohio), to provide a storageabsorbent member consisting of a homogeneous blend of 50%, by weight,hydrogel-forming polymer and 50%, by weight, fibrets.

Structures

As has been laid out in the general part of the description, theabsorbent cores can be constructed in a wide variety of possibilities,provided these cores include an acquisition/distribution region, whichis in liquid communication with an liquid storage region, and provided,that the materials used in these regions satisfy the respectiverequirements. Thus, such cores can be constructed from respectivematerials in a layered arrangement, with the basis weights and sizesadjusted to the requirements of the intended use as laid out in theabove.

A specific core construction, which is useful for baby diapers of thecommonly designated MAXI size, has a rectangular shape with about 450 mmlength and about 100 mm width. Therein, the acquisition/distributionregion cosnsits of a layer of material having a dimension of alsorectangular shape, which covers the complete absorbent core. The liquidstorage region can also be of rectangular shape, also extending over thecomplete size of the absorbent core, underlying as a layer theacquisition distribution region. The thickness of the materials can varythroughout the length and/or the width of the absorbent core, but insimple constructions it is a uniform thickness throughout the absorbentcore.

It is essential for the functioning that the acquisition/distributionmaterial and the storage materials are chosen according to theircapillary suction properties as laid out in the above.

With the specially selected samples as described in the above allrespective distribution material samples can be combined with any of therespective storage materials and provide a suitable performance.

Test Procedures

Unless specified otherwise, the tests are carried out under controlledlaboratory conditions of about 23+/−2° C. and at 50+/−10% relativehumidity. Test specimen are stored under these conditions for at least24 hours before testing.

Synthetic Urine Formulation

Unless specified explicitly, the specific synthetic urine used in thetest methods is commonly known as Jayco SynUrine and is available fromJayco Pharmaceuticals Company of Camp Hill, Pa. The formula for thesynthetic urine is: 2.0 g/: of KCl; 2.0 g/l of Na2SO4; 0.85 g/l of(NH4)H2PO4; 0.15 g/l (NH4)H2PO4; 0.19 g/l of CaCl2; ad 0.23 g/l ofMgCl2. All of the chemicals are of reagent grade. The pH of thesynthetic Urine is in the range of 6.0 to 6.4.

Vertical Wicking Time and Vertical Wicking Capacity

Vertical wicking time is determined by measuring the time taken for acolored test liquid (e.g., synthetic urine) in a reservoir to wick avertical distance of 15 cm through a test strip of foam of specifiedsize. The vertical wicking procedure is detailed in the Test Methodssection of U.S. Pat. No. 5,387,207 (which is incorporated by reference,)supra, but is performed at 31° C. instead of 37° C. A material'svertical wicking capacity for a given height is measured using theVertical Wicking Absorbent Capacity Test also described in the TestMethods section of U.S. Pat. No. 5,387,207, except the test is performedat 31° C. instead of 37° C. Finally, the washing and redrying step inthe referenced patent is not performed. The vertical wicking capacityvalue of note is taken as the capacity achieved at a height of 15 cm atequilibrium. The result is expressed in units of (g/cm²/sec), at aheight of 15 cm.

Simplified Liquid Permeability Test

This Simplified Permeability Test provides a measure for permeabilityfor two special conditions: Either the permeability can be measured fora wide range of porous materials (such as non-wovens made of syntheticfibres, or cellulosic structures) at 100% saturation, or for materials,which reach different degrees of saturation with a proportional changein caliper without being filled with air (respectively the outsidevapour phase), such as the collapsible polymeric foams, for which thepermeability at varying degrees of saturation can readily be measured atvarious thicknesses.

In particular for polymeric foam materials, it has been found useful tooperate the test at an elevated temperature of 31° C., so as to bettersimulate in-use conditions for absorbent articles.

In principle, this tests is based on Darcy's law, according to which thevolumetric flow rate of a liquid through any porous medium isproportional to the pressure gradient, with the proportionality constantrelated to permeability.

Q/A=(k/η)*(ΔP/L)

where:

Q=Volumetric Flow Rate [cm³/s];

A=Cross Sectional Area [cm²];

k=Permeability (cm²) (with 1 Darcy corresponding to 9.869* 10⁻¹³ m²);

η=Viscosity (Poise) [Pa*s];

ΔP/L=Pressure Gradient [Pa/m];

L=caliper of sample [cm].

Hence, permeability can be calculated—for a fixed or given samplecross-sectional area and test liquid viscosity—by measurement ofpressure drop and the volumetric flow rate through the sample:

k=(Q/A)*(L/ΔP)*η

The test can be executed in two modifications, the first referring tothe transplanar permeability (i.e. the direction of flow is essentiallyalong the thickness dimension of the material), the second being thein-plane permeability m(i.e. the direction of flow being in thex-y-direction of the material).

The test set-up for the simplified, transplanar permeability test can besee in FIG. 1 which is a schematic diagram of the overall equipmentand—as an insert diagram—a partly exploded cross-sectional, not to scaleview of the sample cell.

The test set-up comprises a generally circular or cylindrical samplecell (120), having an upper (121) and lower (122) part. The distance ofthese parts can be measured and hence adjusted by means of each threecircumferentially arranged caliper gauges (145) and adjustment screws(140). Further, the equipment comprises several fluid reservoirs (150,154, 156) including a height adjustment (170) for the inlet reservoir(150) as well as tubings (180), quick release fittings (189) forconnecting the sample cell with the rest of the equipment, furthervalves (182, 184, 186, 188). The differential pressure transducer (197)is connected via tubing (180) to the upper pressure detection point(194) and to the lower pressure detection point (196). A Computer device(190) for control of valves is further connected via connections (199)to differential pressure transducer (197), temperature probe (192), andweight scale load cell (198).

The circular sample (110) having a diameter of 1 in (about 2.54 cm) isplaced in between two porous screens (135) inside the sample cell (120),which is made of two 1 in (2.54 cm) inner diameter cylindrical pieces(121, 122) attached via the inlet connection (132) to the inletreservoir (150) and via the outlet connection (133) to the outletreservoir (154) by flexible tubing (180), such as tygon tubing. Closedcell foam gaskets (115) provide leakage protection around the sides ofthe sample. The test sample (110) is compressed to the calipercorresponding to the desired wet compression, which is set to 0.2 psi(about 1.4 kPa) unless otherwise mentioned. Liquid is allowed to flowthrough the sample (110) to achieve steady state flow. Once steady stateflow through the sample (110) has been established, volumetric flow rateand pressure drop are recorded as a function of time using a load cell(198) and the differential pressure transducer (197). The experiment canbe performed at any pressure head up to 80 cm water (about 7.8 kPa),which can be adjusted by the height adjusting device (170). From thesemeasurements, the flow rate at different pressures for the sample can bedetermined.

The equipment is commercially available as a Permeameter such assupplied by Porous Materials, Inc, Ithaca, N.Y., US under thedesignation PMI Liquid Permeameter, such as further described inrespective user manual of 2/97. This equipment includes two StainlessSteel Frits as porous screens (135), also specified in said brochure.The equipment consists of the sample cell (120), inlet reservoir (150),outlet reservoir (154), and waste reservoir (156) and respective fillingand emptying valves and connections, an electronic scale, and acomputerized monitoring and valve control unit (190).

The gasket material (115) is a Closed Cell Neoprene Sponge SNC-1 (Soft),such as supplied by Netherland Rubber Company, Cincinnati, Ohio, US. Aset of materials with varying thickness in steps of {fraction (1/16)}″(about 0.159 cm) should be available to cover the range from {fraction(1/16)}″-½″ (about 0.159 cm to about 1.27 cm) thickness.

Further a pressurized air supply is required, of at least 60 psi (4.1bar), to operate the respective valves. Test fluid is deionized water.The test is then executed by the following steps:

1) Preparation of the test sample(s):

In a preparatory test, it is determined, if one or more layers of thetest sample are required, wherein the test as outlined below is run atthe lowest and highest pressure. The number of layers is then adjustedso as to maintain the flow rate during the test between 0.5 cm³'secondsat the lowest pressure drop and 15 cm³/second at the highest pressuredrop. The flow rate for the sample should be less than the flow rate forthe blank at the same pressure drop. If the sample flow rate exceedsthat of the blank for a given pressure drop, more layers should be addedto decrease the flow rate.

Sample size: Samples are cut to 1″ (about 2.54 cm) diameter, by using anarch punch, such as supplied by McMaster-Carr Supply Company, Cleveland,Ohio, US. If samples have too little internal strength or integrity tomaintain their structure during the required manipulation, aconventional low basis weight support means can be added, such as a PETscrim or net.

Thus, at least two samples (made of the required number of layers each,if necessary) are precut. Then, one of these is saturated in deionizedwater at the temperature the experiment is to be performed (70° F., (31°C.) unless otherwise noted).

The caliper of the wet sample is measured (if necessary after astabilization time of 30 seconds) under the desired compression pressurefor which the experiment will be run by using a conventional calipergauge (such as supplied by AMES, Waltham, Mass., US) having a pressurefoot diameter of 1⅛″ (about 2.86 cm), exerting a pressure of 0.2 psi(about 1.4 kPa) on the sample (110), unless otherwise desired.

An appropriate combination of gasket materials is chosen, such that thetotal thickness of the gasketing foam (115) is between 150 and 200% ofthe thickness of the wet sample (note that a combination of varyingthicknesses of gasket material may be needed to achieve the overalldesired thickness). The gasket material (115) is cut to a circular sizeof 3″ in diameter, and a 1 inch (2.54 cm) hole is cut into the center byusing the arch punch.

In case, that the sample dimensions change upon wetting, the sampleshould be cut such that the required diameter is taken in the wet stage.This can also be assessed in this preparatory test, with monitoring ofthe respective dimensions. If these change such that either a gap isformed, or the sample forms wrinkles which would prevent it fromsmoothly contacting the porous screens or frits, the cut diameter shouldbe adjusted accordingly.

The test sample (110) is placed inside the hole in the gasket foam(115), and the composite is placed on top of the bottom half of thesample cell, ensuring that the sample is in flat, smooth contact withthe screen (135), and no gaps are formed at the sides.

The top of the test cell (121) is laid flat on the lab bench (or anotherhorizontal plane) and all three caliper gauges (145) mounted thereon arezeroed.

The top of the test cell (121) is then placed onto the bottom part (122)such that the gasket material (115) with the test sample (110) lays inbetween the two parts. The top and bottom part are then tightened by thefixation screws (140), such that the three caliper gauges are adjustedto the same value as measured for the wet sample under the respectivepressure in the above.

2) To prepare the experiment, the program on the computerized unit (190)is started and sample identification, respective pressure etc. areentered.

3) The test will be run on one sample (110) for several pressure cycles,with the first pressure being the lowest pressure. The results of theindividual pressure runs are put on different result files by thecomputerized unit (190). Data are taken from each of these files for thecalculations as described below. (A different sample should be used forany subsequent runs of the material.)

4) The inlet liquid reservoir (150) is set to the required height andthe test is started on the computerized unit (190).

5) Then, the sample cell (120) is positioned into the permeameter unitwith Quick Disconnect fittings (189).

6) The sample cell (120) is filled by opening the vent valve (188) andthe bottom fill valves (184, 186). During this step, care must be takento remove air bubbles from the system, which can be achieved by turningthe sample cell vertically, forcing air bubbles—if present—to exit thepermeameter through the drain.

Once the sample cell is filled up to the tygon tubing attached to thetop of the chamber (121), air bubbles are removed from this tubing intothe waste reservoir (156).

7) After having carefully removed air bubbles, the bottom fill valves(184, 186) are closed, and the top fill (182) valve is opened, so as tofill the upper part, also carefully removing all air bubbles.

8) The fluid reservoir is filled with test fluid to the fill line (152).

Then the flow is started through the sample by initiating thecomputerized unit (190).

After the temperature in the sample chamber has reached the requiredvalue, the experiment is ready to begin.

Upon starting the experiment via the computerized unit (190), the liquidoutlet flow is automatically diverted from the waste reservoir (156) tothe outlet reservoir (154), and pressure drop, and temperature aremonitored as a function of time for several minutes.

Once the program has ended, the computerized unit provides the recordeddata (in numeric and/or graphical form).

If desired, the same test sample can be used to measure the permeabilityat varying pressure heads, with thereby increasing the pressure from runto run.

The equipment should be cleaned every two weeks, and calibrated at leastonce per week, especially the frits, the load cell, the thermocouple andthe pressure transducer, thereby following the instructions of theequipment supplier.

The differential pressure is recorded via the differential pressuetransducer connected to the pressure probes measurement points (194,196) in the top and bottom part of the sample cell. Since there may beother flow resistances within the chamber adding to the pressure that isrecorded, each experiment must be corrected by a blank run. A blank runshould be done at 10, 20, 30, 40, 50, 60, 70, 80 cm requested pressure,each day. The permeameter will output a Mean Test Pressure for eachexperiment and also an average flow rate.

For each pressure that the sample has been tested at, the flow rate isrecorded as Blank Corrected Pressure by the computerized unit (190),which is further correcting the Mean Test Pressure (Actual Pressure) ateach height recorded pressure differentials to result in the CorrectedPressure. This Corrected Pressure is the DP that should be used in thepermeability equation below.

Permeability can then be calculated at each requested pressure and allpermeabilities should be averaged to determine the k for the materialbeing tested.

Three measurements should be taken for each sample at each head and theresults averaged and the standard deviation calculated. However, thesame sample should be used, permeability measured at each head, and thena new sample should be used to do the second and third replicates.

The measuring of the in-plane permeability under the same conditions asthe above described transplanar permeability, can be achieved bymodifying the above equipment such as schematically depicted in FIGS. 2Aand 2B showing the partly exploded, not to scale view of the sample cellonly. Equivalent elements are denoted equivalently, such that the samplecell of FIG. 2 is denoted (210), correlating to the numeral (110) ofFIG. 1, and so on. Thus, the transplanar simplified sample cell (120) ofFIG. 1 is replaced by the in-plane simplified sample cell (220), whichis designed so that liquid can flow only in one direction (eithermachine direction or cross direction depending on how the sample isplaced in the cell). Care should be taken to minimize channeling ofliquid along the walls (wall effects), since this can erroneously givehigh permeability reading. The test procedure is then executed quiteanalogous to the transplanar simplified test.

The sample cell (220) is designed to be positioned into the equipmentessentially as described for the sample cell (120) in the abovetransplanar test, except that the filling tube is directed to the inletconnection (232) the bottom of the cell (220). FIG. 2A shows a partlyexploded view of the sample cell, and FIG. 2B a cross-sectional viewthrough the sample level.

The test cell (220) is made up of two pieces: a bottom piece (225) whichis like a rectangular box with flanges, and a top piece (223) that fitsinside the bottom piece (225) and has flanges as well. The test sampleis cut to the size of 2″ in×2″ in (about 5.1 cm by 5.1 cm) and is placedinto the bottom piece. The top piece (223) of the sample chamber is thenplaced into the bottom piece (225) and sits on the test sample (210). Anincompressible neoprene rubber seal (224) is attached to the upper piece(223) to provide tight sealing. The test liquid flows from the inletreservoir to the sample space via Tygon tubing and the inlet connection(232) further through the outlet connection (233) to the outletreservoir. As in this test execution the temperature control of thefluid passing through the sample cell can be insufficient due to lowerflow rates, the sample is kept at the desired test temperature by theheating device (226), whereby thermostated water is pumped through theheating chamber (227). The gap in the test cell is set at the calipercorresponding to the desired wet compression, normally 0.2 psi ( about1.4 kPa). Shims (216) ranging in size from 0.1 mm to 20.0 mm are used toset the correct caliper, optionally using combinations of several shims.

At the start of the experiment, the test cell (220) is rotated 90°(sample is vertical) and the test liquid allowed to enter slowly fromthe bottom. This is necessary to ensure that all the air is driven outfrom the sample and the inlet/outlet connections (232/233). Next, thetest cell (220) is rotated back to its original position so as to makethe sample (210) horizontal. The subsequent procedure is the same asthat described earlier for transplanar permeability, i.e. the inletreservoir is placed at the desired height, the flow is allowed toequilibrate, and flow rate and pressure drop are measured. Permeabilityis calculated using Darcy's law. This procedure is repeated for higherpressures as well.

For samples that have very low permeability, it may be necessary toincrease the driving pressure, such as by extending the height or byapplying additional air pressure on the reservoir in order to get ameasurable flow rate. In plane permeability can be measuredindependently in the machine and cross directions, depending on how thesample is placed in the test cell.

General Liquid Permeability Test

The generalized permeability test can measure permeability as a functionof saturation for any porous material. The principle of the tests issimilar to the one for the Simplified Test, with the essentialdifference being that the sample is loaded with a defined amount of airin addition to the liquid loading, resulting in a fixed degree ofsaturation. This is achieved by the test arrangement as schematicallydepicted in FIG. 3 showing the principles as well as the specifics forthe General Transplanar Permeability, and in FIG. 4, showing thedifferences for the General In-plane Permeability. Unreferenced numeralscorrespond to the respective numerals of FIG. 1 (e.g., waste reservoir(356) corresponds to waste reservoir (156) etc.).

Therein, also the sample cell (320/420) is mounted with fixation (341,not shown in FIG. 4) on a height adjustment device (372), in addition tothe inlet reservoir (350) being height adjustable by a means (370). Thisinlet reservoir defines a first height difference (357) relative to theoutlet reservoir (354), which relates to the differential pressure Δp(which denotes the pressure differential for calculating thepermeability). This inlet reservoir (350) defines a second heightdifference (359) relative to the sample height which relates to thedifferential pressure Δp(c), which denotes the pressure differentiallinked to the saturation in the sample, whereby higher capillary suctiontypically correlates to lower saturation.

The experiment is started at low ΔPc (close to zero cm of water) atwhich the sample will be at 100% saturation. Liquid flows through thesample due to the applied pressure drop Δp(c) (inlet reservoirheight—outlet reservoir height). At steady state, the uptake of liquidin the outlet reservoir is measured as a function of time. Permeabilitycan be calculated from the pressure drop and the volumetric flow ratedata using Darcy's law. The exact degree of saturation can be obtainedfrom the weight of the wet sample after the test compared to the drysample before the test.

In order to measure the permeability at saturation below 100%, a newtest sample is first brought to 100% saturation as described in theparagraph above. Next, the sample is moved to a higher height (10 cm forexample) and is allowed to equilibrate at that height. During this time,liquid continuously flows from the inlet to the outlet reservoir. Thesaturation in the sample will decrease with time. When steady state isreached, i.e. when the uptake versus time plot is linear, the flow rate,pressure drop and saturation are measured as described above. Thisprocedure is repeated for several sample heights using new samples.

It may be necessary to increase the pressure drop between the inlet andoutlet reservoirs as the saturation decreases in order to get ameasurable flow rate. This is because, for most porous materials,permeability decreases steeply with decreasing saturation. It isnecessary to ensure that the pressure drop between the inlet and outletreservoirs is much smaller than the capillary suction.

It is necessary to use wide liquid reservoirs (352, 354) in order toensure that the liquid level does not change significantly while waitingfor steady state to be reached.

This test gives permeability versus saturation for the desorption cycle,that is the sample has higher saturation to start with. Whilst of coursepermeability data can be generated for the absorption cycle, theseshould not be used in present evaluations, as some hysteresis effectsmight occur.

The sample cell (320) for the general transplanar permeability testdiffers from sample cell (120) of the simplified transplanarpermeability test essentially in that it comprises two frits (335)arranged on top and underneath the sample (310). For the frits (335) itis necessary to ensure that most of the resistance to flow is offered bythe sample and the frit resistance is negligible. A fine pored, thinmembrane over a coarse frit allows measurements up to high heightswithout offering significant resistance to flow. The frits should beselected so as to have a sufficiently high bubble point pressurecorresponding to more than about 200 cm water height, but at the sametime providing low flow resistance. This can well be achieved byselecting sufficiently thin membranes of the require bubble pointpressure overlying a more open support structure.

For the general permeability tests, care must be taken, that the air isallowed to contact the sample via the side surfaces, so as to allowvarying degrees of saturation depending on the Δp(c). Thus, the samplecell design is essentially identical to the test cell of the simplifiedtransplanar test, except, that the foam gasketing material is removed,and the arrangement to adjust the gap between the top and the bottomparts replaced by a constant pressure generating device, such as aweight (317) to maintain (together with the weight of the top piece(321)) the sample under the desired pressure, of 0.2 psi (about 1.4 kPa)unless otherwise desired.

For the general in-plane permeability test the sample cell (420) isshown in FIG. 4, which is a design being derived from the simplifiedin-plane test and the principles as described in the above. Thus, thefluid in entering the sample cell (420) via the fluid inlet (432) andoutlet (433), which are connected to the membranes (435), such as fritsof the type as described above (for frits 335). The test sample (410) ispositioned with its ends overlaying the two frits, but not with thecenter part of 2 in by 2 in (about 5.1 cm by 5.1 cm) whereby wrinklesand gaps between the sample and the membranes have to be avoided. Thetest sample (410) is placed between the upper and lower part of thesample cell (420), with the weight (417) being used to adjust thepressure under which the experiment is run (0.2 psi (about 1.4 kPa)unless otherwise desired and denoted). Also, the sample is kept aconstant temperature via the heating device (426), e.g. by pumpingconstant temperature water through the heating chamber (427).

Also for this set up, the possibility of air entering into the samplevia the side surfaces is essential to allow the varying degrees ofsaturation.

Liquid Viscosity

The liquid viscosity is an important input parameter for the abovedetermination, and should be taken for the respective fluid for therespective temperature, either from well known tables, or equations, ormeasured via well established measurement procedures.

Capillary Sorption

Purpose

The purpose of this test is to measure the capillary sorption absorbentcapacity, as a function of height, of storage absorbent members of thepresent invention. (The test is also used to measure the capillarysorption absorbent capacity, as a function of height, of the highsurface area materials—i.e., without osmotic absorbent, such ashydrogel-forming absorbent polymer, or other optional materials utilizedin the absorbent member. Nonetheless, the discussion that followsdiscusses the Capillary Sorption method as it pertains to measuring anentire storage absorbent member.) Capillary sorption is a fundamentalproperty of any absorbent that governs how liquid is absorbed into theabsorbent structure. In the Capillary Sorption experiment, capillarysorption absorbent capacity is measured as a function of fluid pressuredue to the height of the sample relative to the test fluid reservoir.

The method for determining capillary sorption is well recognized. SeeBurgeni, A. A. and Kapur, C., “Capillary Sorption Equilibria in FiberMasses,” Textile Research Journal, 37 (1967), 356-366; Chatterjee, P.K., Absorbency, Textile Science and Technology 7, Chapter II, pp 29-84,Elsevier Science Publishers B.V, 1985; and U.S. Pat. No. 4,610,678,issued Sep. 9, 1986 to Weisman et al. for a discussion of the method formeasuring capillary sorption of absorbent structures. The disclosure ofeach of these references is incorporated by reference herein.

Principle

A porous glass frit is connected via an uninterrupted column of fluid toa fluid reservoir on a balance. The sample is maintained under aconstant confining weight during the experiment. As the porous structureabsorbs fluid upon demand, the weight loss in the balance fluidreservoir is recorded as fluid uptake, adjusted for uptake of the glassfrit as a function of height and evaporation. The uptake or capacity atvarious capillary suctions (hydrostatic tensions or heights) ismeasured. Incremental absorption occurs due to the incremental loweringof the frit (i.e., decreasing capillary suction).

Time is also monitored during the experiment to enable calculation ofinitial effective uptake rate (g/g/h) at a 200 cm height.

Reagents

Test Liquid: Synthetic urine is prepared by completely dissolving thefollowing materials in distilled water.

Compound F.W. Concentration (g/L) KCl 74.6 2.0 Na₂SO₄ 142 2.0 (NH₄)H₂PO₄115 0.85 (NH₄)₂HPO₄ 132 0.15 CaCl₂.2H₂O 147 0.25 MgCl₂.6H₂O 203 0.5

General Description of Apparatus Set Up

The Capillary Sorption equipment, depicted generally as 520 in FIG. 2A,used for this test is operated under TAPPI conditions (50% RH, 25° C.).A test sample is placed on a glass frit shown in FIG. 2A as 502 that isconnected via a continuous column of test liquid (synthetic urine) to abalance liquid reservoir, shown as 506, containing test liquid. Thisreservoir 506 is placed on a balance 507 that is interfaced with acomputer (not shown). The balance should be capable of reading to 0.001g; such a balance is available from Mettler Toledo as PR1203(Hightstown, N.J.). The glass frit 502 is placed on a vertical slide,shown generally in FIG. 2A as 501, to allow vertical movement of thetest sample to expose the test sample to varying suction heights. Thevertical slide may be a rodless actuator which is attached to a computerto record suction heights and corresponding times for measuring liquiduptake by the test sample. A preferred rodless actuator is availablefrom Industrial Devices (Novato, Calif.) as item202X4X34N-1D4B-84-P-C-S-E, which may be powered by motor drive ZETA6104-83-135, available from CompuMotor (Rohnert, Calif.). Where data ismeasured and sent from actuator 501 and balance 507, capillary sorptionabsorbent capacity data may be readily generated for each test sample.Also, computer interface to actuator 501 may allow for controlledvertical movement of the glass frit 502. For example, the actuator maybe directed to move the glass frit 502 vertically only after“equilibrium” (as defined below) is reached at each suction height.

The bottom of glass frit 502 is connected to Tygon® tubing 503 thatconnects the frit 505 to three-way drain stopcock 509. Drain stopcock509 is connected to liquid reservoir 505 via glass tubing 504 andstopcock 510. (The stopcock 509 is open to the drain only duringcleaning of the apparatus or air bubble removal.) Glass tubing 511connects fluid reservoir 505 with balance fluid reservoir 506, viastopcock 510. Balance liquid reservoir 506 consists of a lightweight 12cm diameter glass dish 506A and cover 506B. The cover 506B has a holethrough which glass tubing 511 contacts the liquid in the reservoir 506.The glass tubing 511 must not contact the cover 506B or an unstablebalance reading will result and the test sample measurement cannot beused.

The glass frit diameter must be sufficient to accommodate thepiston/cylinder apparatus, discussed below, for holding the test sample.The glass frit 502 is jacketed to allow for a constant temperaturecontrol from a heating bath. The frit is a 350 ml fritted disc funnelspecified as having 4 to 5.5 μm pores, available from Coming Glass Co.(Coming, N.Y.) as #36060-350F. The pores are fine enough to keep thefrit surface wetted at capillary suction heights specified (the glassfrit does not allow air to enter the continuous column of test liquidbelow the glass frit).

As indicated, the frit 502 is connected via tubing to fluid reservoir505 or balance liquid reservoir 506, depending on the position ofthree-way stopcock 510.

Glass frit 502 is jacketed to accept water from a constant temperaturebath. This will ensure that the temperature of the glass frit is kept ata constant temperature of 88° F. (31° C.) during the testing procedure.As is depicted in FIG. 2A, the glass frit 502 is equipped with an inletport 502A and outlet port 502B, which make a closed loop with acirculating heat bath shown generally as 508. (The glass jacketing isnot depicted in FIG. 2A. However, the water introduced to the jacketedglass frit 502 from bath 508 does not contact the test liquid and thetest liquid is not circulated through the constant temperature bath. Thewater in the constant temperature bath circulates through the jacketedwalls of the glass frit 502.)

Reservoir 506 and balance 507 are enclosed in a box to minimizeevaporation of test liquid from the balance reservoir and to enhancebalance stability during performance of the experiment. This box, showngenerally as 512, has a top and walls, where the top has a hole throughwhich tubing 511 is inserted.

The glass frit 502 is shown in more detail in FIG. 2B. FIG. 2B is across-sectional view of the glass frit, shown without inlet port 502Aand outlet port 502B. As indicated, the glass frit is a 350 ml fritteddisc funnel having specified 4 to 5.5 μm pores. Referring to FIG. 2B,the glass frit 502 comprises a cylindrical jacketed funnel designated as550 and a glass frit disc shown as 560. The glass frit 502 furthercomprises a cylinder/piston assembly shown generally as 565 (whichcomprises cylinder 566 and piston 568), which confines the test sample,shown as 570, and provides a small confining pressure to the testsample. To prevent excessive evaporation of test liquid from the glassfrit disc 560, a Teflon ring shown as 562 is placed on top of the glassfrit disc 560. The Teflon® ring 562 is 0.0127 cm thick (available assheet stock from McMasterCarr as #8569K16 and is cut to size) and isused to cover the frit disc surface outside of the cylinder 566, andthus minimizes evaporation from the glass frit. The ring outer diameterand inner diameter is 7.6 and 6.3 cm, respectively. The inner diameterof the Teflon® ring 562 is about 2 mm less than the outer diameter ofcylinder 566. A Viton® O-ring (available from McMasterCarr as#AS568A-150 and AS568A-151) 564 is placed on top of Teflon® ring 562 toseal the space between the inner wall of cylindrical jacketed funnel 550and Teflon® ring 562, to further assist in prevention of evaporation. Ifthe O-ring outer diameter exceeds the inner diameter of cylindricaljacketed funnel 550, the O-ring diameter is reduced to fit the funnel asfollows: the O-ring is cut open, the necessary amount of O-ring materialis cut off, and the O-ring is glued back together such that the O-ringcontacts the inner wall of the cylindrical jacketed funnel 550 allaround its periphery.

As indicated, a cylinder/piston assembly shown generally in FIG. 2B as565 confines the test sample and provides a small confining pressure tothe test sample 570. Referring to FIG. 2C, assembly 565 consists of acylinder 566, a cup-like Teflon® piston indicated by 568 and, whennecessary, a weight or weights (not shown) that fits inside piston 568.(Optional weight will be used when necessary to adjust the combinedweight of the piston and the optional weight so a confining pressure of0.2 psi is attained depending on the test sample's dry diameter. This isdiscussed below.) The cylinder 566 is Lexan® bar stock and has thefollowing dimensions: an outer diameter of 7.0 cm, an inner diameter of6.0 cm and a height of 6.0 cm. The Teflon® piston 568 has the followingdimensions: an outer diameter that is 0.02 cm less than the innerdiameter of cylinder 566. As shown in FIG. 2D, the end of the piston 568that does not contact the test sample is bored to provide a 5.0 cmdiameter by about 1.8 cm deep chamber 590 to receive optional weights(dictated by the test sample's actual dry diameter) required to attain atest sample confining pressure of 0.2 psi (1.4 kPa). In other words, thetotal weight of the piston 568 and any optional weights (not shown infigures) divided by the test sample's actual diameter (when dry) shouldbe such that a confining pressure of 0.2 psi is attained. Cylinder 566and piston 568 (and optional weights) are equilibrated at 31° C. for atleast 30 minutes prior to conducting the capillary sorption absorbentcapacity measurement.

A non-surfactant treated or incorporated apertured film (14 cm×14 cm)(not shown) is used to cover the glass frit 502 during CapillarySorption experiments to minimize air destablization around the sample.Apertures are large enough to prevent condensation from forming on theunderside of the film during the experiment.

Test Sample Preparation

The test sample can be obtained by punching out a 5.4 cm diametercircular-shaped structure from a storage absorbent member. When themember is a component of an absorbent article, other components of thearticle must be removed prior to testing. In those situations where themember cannot be isolated from other components of the article withoutsignificantly altering its structure (e.g., density, relativedisposition of the component materials, physical properties ofconstituent materials, etc.) or where the member is not a component ofan absorbent article, the test sample is prepared by combining all thematerials that constitute the member such that the combination isrepresentative of the member in question. The test sample is a 5.4 cmdiameter circle and is obtained by cutting with an arch punch.

The dry weight of the test sample (used below to calculate capillarysorption absorbent capacity) is the weight of the test sample preparedas above under ambient conditions.

Experimental Set Up

1. Place a clean, dry glass frit 502 in a funnel holder attached to thevertical slide 501. Move the funnel holder of the vertical slide suchthat the glass frit is at the 0 cm height.

2. Set up the apparatus components as shown in FIG. 2A, as discussedabove.

3. Place 12 cm diameter balance liquid reservoir 506 on the balance 507.Place plastic lid 506B over this balance liquid reservoir 506 and aplastic lid over the balance box 512 each with small holes to allow theglass tubing 511 to fit through. Do not allow the glass tubing to touchthe lid 506B of the balance liquid reservoir or an unstable balancereading will result and the measurement cannot be used.

4. Stopcock 510 is closed to tubing 504 and opened to glass tubing 511.Fluid reservoir 505, previously filled with test fluid, is opened toallow test fluid to enter tubing 511, to fill balance fluid reservoir506.

5. The glass frit 502 is leveled and secured in place. Also, ensure thatthe glass frit is dry.

6. Attach the Tygon® tubing 503 to stopcock 509. (The tubing should belong enough to reach the glass frit 502 at its highest point of 200 cmwith no kinks.) Fill this Tygon® tubing with test liquid from liquidreservoir 505.

7. Attach the Tygon® tubing 503 to the level glass frit 502 and thenopen stopcock 509 and stopcock 510 leading from fluid reservoir 505 tothe glass frit 502. (Stopcock 510 should be closed to glass tubing 511.)The test liquid fills the glass frit 502 and removes all trapped airduring filling of the level glass frit. Continue to fill until the fluidlevel exceeds the top of the glass frit disc 560. Empty the funnel andremove all air bubbles in the tubing and inside the funnel. Air bubblesmay be removed by inverting glass frit 502 and allowing air bubbles torise and escape through the drain of stopcock 509. (Air bubblestypically collect on the bottom of the glass frit disc 560.) Relevel thefrit using a small enough level that it will fit inside the jacketedfunnel 550 and onto the surface of glass frit disc 560.

8. Zero the glass frit with the balance liquid reservoir 506. To dothis, take a piece of Tygon® tubing of sufficient length and fill itwith the test liquid. Place one end in the balance liquid reservoir 506and use the other end to position the glass frit 502. The test liquidlevel indicated by the tubing (which is equivalent to the balance liquidreservoir level) is 10 mm below the top of the glass frit disc 560. Ifthis is not the case, either adjust the amount of liquid in thereservoir or reset the zero position on the vertical slide 501.

9. Attach the outlet and inlet ports from the temperature bath 508 viatubing to the inlet and outlet ports 502A and 502B, respectively, of theglass frit. Allow the temperature of the glass frit disc 560 to come to31° C. This can be measured by partially filling the glass frit withtest liquid and measuring its temperature after it has reachedequilibrium temperature. The bath will need to be set a bit higher than31° C. to allow for the dissipation of heat during the travel of waterfrom the bath to the glass frit.

10.The glass frit is equilibrated for 30 minutes.

Capillary Sorption Parameters

The following describes a computer program that will determine how longthe glass frit remains at each height.

In the capillary sorption software program, a test sample is at somespecified height from the reservoir of fluid. As indicated above, thefluid reservoir is on a balance, such that a computer can read thebalance at the end of a known time interval and calculate the flow rate(Delta reading/time interval) between the test sample and reservoir. Forpurposes of this method, the test sample is considered to be atequilibrium when the flow rate is less than a specified flow rate for aspecified number of consecutive time intervals. It is recognized, thatfor certain material, actual equilibrium may not be reached when thespecified “EQUILIBRIUM CONSTANT” is reached. The time interval betweenreadings is 5 seconds.

The number of readings in the delta table is specified in the capillarysorption menu as “EQUILIBRIUM SAMPLES”. The maximum number of deltas is500. The flow rate constant is specified in the capillary sorption menuas “EQUILIBRIUM CONSTANT”.

The Equilibrium Constant is entered in units of grams/sec, ranging from0.0001 to 100.000.

The following is a simplified example of the logic. The table shows thebalance reading and Delta Flow calculated for each Time Interval.

Equilibrium Samples=3

Equilibrium Constant=0.0015

Balance Delta Time Value Flow Interval (g) (g/sec) 0 0 1 0.090 0.0180 20.165 0.0150 3 0.225 0.0120 4 0.270 0.0090 5 0.295 0.0050 6 0.305 0.00207 0.312 0.0014 8 0.316 0.0008 9 0.318 0.0004

Delta Table: Time 0 1 2 3 4 5 6 7 8 9 Delta1 9999 0.0180 0.0180 0.01800.0090 0.0090 0.0090 0.0014 0.0014 0.0014 Delta2 9999 9999 0.0150 0.01500.0150 0.0050 0.0050 0.0050 0.0008 0.0008 Delta3 9999 9999 9999 0.01200.0120 0.0120 0.0020 0.0020 0.0020 0.0004

The equilibrium uptake for the above simplified example is 0.318 gram.

The following is the code in C language used to determine equilibriumuptake:

/* takedata.c */ int take_data(int equil_samples,doubleequilibrium_constant) { double delta; static double deltas[500]; /*table to store up to 500 deltas */ double value; double prev_value;clock_t next_time; int i; for (i=0; i<equil_samples; i++)  deltas[i] =9999.; /* initialize all values in the delta table to 9999. gms/sec */delta_table_index = 0; /* initialize where in the table to store thenext delta */ equilibrium_reached = 0; /* initialize flag to indicateequilibrium has not been reached */ next_time = clock( ); /* initializewhen to take the next reading */ prev_reading = 0.; /* initialize thevalue of the previous reading from the balance */ while(!equilibrium_reached) {  /* start of loop for checking for equilibrium*/  next_time += 5000 L; /* calculate when to take next reading */ while (clock( ) < next_time); /* wait until 5 seconds has elasped fromprev reading */  value = get_balance_reading( ); /* read the balance ingrams */  delta = fabs(prev_value - value)/5.0; /* calculate absolutevalue of flow in last 5 seconds */  prev_value = value; /* store currentvalue for next loop */  deltas[delta_table_index] = delta; /* storecurrent delta value in the table of deltas */  delta_table_index++; /*increment pointer to next position in table */  if (delta_table_index ==equil_samples) /* when the number of deltas = the number of */  delta_table_index = 0; /* equilibrium samples specified, /* /* resetthe pointer to the start of the table. This way */ /* the table alwayscontains the last xx current samples. */  equilibrium_reached = 1; /*set the flag to indicate equilibrium is reached */  for (i=0; i <equil_samples; i++) /* check all the values in the delta table */   if(deltas[i] >= equilibrium_constant) /* if any value is > or = to theequilibrium constant */    equilibrium_reached = 0; /* set theequlibrium flag to 0 (not at equilibrium) */  } /* go back to the startof the loop */ }

Capillary Sorption Parameters

Load Description (Confining Pressure): 0.2 psi load

Equilibrium Samples (n): 50

Equilibrium Constant: 0.0005 g/sec

Setup Height Value: 100 cm

Finish Height Value: 0 cm

Hydrostatic Head Parameters: 200, 180, 160, 140, 120, 100, 90, 80, 70,60, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5 and 0 cm.

The capillary sorption procedure is conducted using all the heightsspecified above, in the order stated, for the measurement of capillarysorption absorbent capacity. Even if it is desired to determinecapillary sorption absorbent capacity at a particular height (e.g., 35cm), the entire series of hydrostatic head parameters must be completedin the order specified. Although all these heights are used inperformance of the capillary sorption test to generate capillarysorption isotherms for a test sample, the present disclosure describesthe storage absorbent members in terms of their absorbent properties atspecified heights of 200, 140, 100, 50, 35 and 0 cm.

Capillary Sorption Procedure

1) Follow the experimental setup procedure.

2) Make sure the temperature bath 508 is on and water is circulatingthrough the glass frit 502 and that the glass frit disc 560 temperatureis 31° C.

3) Position glass frit 502 at 200 cm suction height. Open stopcocks 509and 510 to connect glass frit 502 with the balance liquid reservoir 506.(Stopcock 510 is closed to liquid reservoir 505.) Glass frit 502 isequilibrated for 30 minutes.

4) Input the above capillary sorption parameters into the computer.

5) Close stopcocks 509 and 510.

6) Move glass frit 502 to the set up height, 100 cm.

7) Place Teflon® ring 562 on surface of glass frit disc 560. Put O-ring564 on Teflon® ring. Place pre-heated cylinder 566 concentrically on theTeflon® ring. Place test sample 570 concentrically in cylinder 566 onglass frit disc 560. Place piston 568 into cylinder 566. Additionalconfining weights are placed into piston chamber 590, if required.

8) Cover the glass frit 502 with apertured film.

9) The balance reading at this point establishes the zero or tarereading.

10) Move the glass frit 502 to 200 cm.

11) Open stopcocks 509 and 510 (stopcock 510 is closed to fluidreservoir 505) and begin balance and time readings.

Glass Frit Correction (Blank Correct Uptake)

Since the glass frit disc 560 is a porous structure, the glass frit(502) capillary sorption absorption uptake (blank correct uptake) mustbe determined and subtracted to get the true test sample capillarysorption absorption uptake. The glass frit correction is performed foreach new glass frit used. Run the capillary sorption procedure asdescribed above, except without test sample, to obtain the BlankUptake(g). The elapsed time at each specified height equals the BlankTime(s).

Evaporation Loss Correction

1) Move the glass frit 502 to 2 cm above zero and let it equilibrate atthis height for 30 minutes with open stopcocks 509 and 510 (closed toreservoir 505).

2) Close stopcocks 509 and 510.

3) Place Teflon® ring 562 on surface of glass frit disc 560. Put O-ring564 on Teflon® ring. Place pre-heated cylinder 566 concentrically on theTeflon® ring. Place piston 568 into cylinder 566. Place apertured filmon glass frit 502.

4) Open stopcocks 509 and 510 (closed to reservoir 505) and recordbalance reading and time for 3.5 hours. Calculate Sample Evaporation(g/hr) as follows:

[balance reading at 1 hr−balance reading at 3.5 hr]/2.5 hr

Even after taking all the above precautions, some evaporative loss willoccur, typically around 0.10 gm/hr for both the test sample and the fritcorrection. Ideally, the sample evaporation is measured for each newlyinstalled glass frit 502.

Cleaning the Equipment

New Tygon® tubing 503 is used when a glass frit 502 is newly installed.Glass tubing 504 and 511, fluid reservoir 505, and balance liquidreservoir 506 are cleaned with 50% Clorox Bleach® in distilled water,followed by distilled water rinse, if microbial contamination isvisible.

a. Cleaning After Each Experiment

At the end of each experiment (after the test sample has been removed),the glass frit is forward flushed (i.e., test liquid is introduced intothe bottom of the glass frit) with 250 ml test liquid from liquidreservoir 505 to remove residual test sample from the glass frit discpores. With stopcocks 509 and 510 open to liquid reservoir 505 andclosed to balance liquid reservoir 506, the glass frit is removed fromits holder, turned upside down and is rinsed out first with test liquid,followed by rinses with acetone and test liquid (synthetic urine).During rinsing, the glass frit must be tilted upside down and rinsefluid is squirted onto the test sample contacting surface of the glassfrit disc. After rinsing, the glass frit is forward flushed a secondtime with 250 ml test liquid (synthetic urine). Finally, the glass fritis reinstalled in its holder and the frit surface is leveled.

b. Monitoring Glass Frit Performance

Glass frit performance must be monitored after each cleaning procedureand for each newly installed glass frit, with the glass frit set up at 0cm position. 50 ml of test liquid are poured onto the leveled glass fritdisc surface (without Teflon® ring, O-ring and the cylinder/pistoncomponents). The time it takes for the test fluid level to drop to 5 mmabove the glass frit disc surface is recorded. A periodic cleaning mustbe performed if this time exceeds 4.5 minutes.

c. Periodic Cleaning

Periodically, (see monitoring frit performance, above) the glass fritsare cleaned thoroughly to prevent clogging. Rinsing fluids are distilledwater, acetone, 50% Clorox Bleach® in distilled water (to removebacterial growth) and test liquid. Cleaning involves removing the glassfrit from the holder and disconnecting all tubing. The glass frit isforward flushed (i.e., rinse liquid is introduced into the bottom of theglass frit) with the frit upside down with the appropriate fluids andamounts in the following order:

1. 250 ml distilled water.

2. 100 ml acetone.

3. 250 ml distilled water.

4. 100 ml 50:50 Clorox®/distilled water solution.

5. 250 ml distilled water.

6. 250 ml test fluid.

The cleaning procedure is satisfactory when glass frit performance iswithin the set criteria of fluid flow (see above) and when no residue isobservable on the glass frit disc surface. If cleaning can not beperformed successfully, the frit must be replaced.

Calculations

The computer is set up to provide a report consisting of the capillarysuction height in cm, time, and the uptake in grams at each specifiedheight. From this data, the capillary suction absorbent capacity, whichis corrected for both the frit uptake and the evaporation loss, can becalculated. Also, based on the capillary suction absorbent capacity at 0cm, the capillary absorption efficiency can be calculated at thespecified heights. In addition, the initial effective uptake rate at 200cm is calculated.

Blank Correct Uptake${{Blank}\quad {Correct}\quad {Uptake}\quad (g)} = {{{Blank}\quad {Uptake}\quad (g)} - \frac{{Blank}\quad {Time}\quad (s)*{Sample}\quad {{Evap}.\quad \left( {g\text{/}{hr}} \right)}}{3600\quad \left( {s\text{/}{hr}} \right)}}$

Capillary Suction Absorbent Capacity (“CSAC”)${{CSAC}\quad \left( {g\text{/}g} \right)} = \frac{{{Sample}\quad {Uptake}\quad (g)} - \frac{{Sample}\quad {Time}\quad (s)*{Sample}\quad {{Evap}.\quad \left( {g\text{/}{hr}} \right)}}{3600\quad s\text{/}{hr}} - {{Blank}\quad {Correct}\quad {Uptake}\quad (g)}}{{Dry}\quad {Weight}\quad {of}\quad {Sample}\quad (g)}$

Initial Effective Uptake Rate at 200 cm (“IEUR”)${{IEUR}\quad \left( {g\text{/}g\text{/}{hr}} \right)} = \frac{{CSAC}\quad {at}\quad 200\quad {cm}\quad \left( {g\text{/}g} \right)}{{Sample}\quad {Time}\quad {at}\quad 200\quad {cm}\quad (s)}$

Reporting

A minimum of two measurements should be taken for each sample and theuptake averaged at each height to calculate Capillary Sorption AbsorbentCapacity (CSAC) for a given absorbent member or a given high surfacearea material.

With these data, the respective values can be calculated:

The Capillary Sorption Desorption Height at which the material hasreleased x % of its capacity at 0 cm (i.e. of CSAC 0), (CSDH x)expressed in cm;

The Capillary Sorption Absorption Height at which the material hasabsorbed y % of its capacity at 0 cm (i.e. of CSAC 0), (CSAH y)expressed in cm;

The Capillary Sorption Absorbent Capacity at a certain height z (CSAC z)expressed in units of g {of fluid}/g {of material}; especially at theheight zero (CSAC 0), and at heights of 35 cm, 40 cm, etc

The Capillary Sorption Absorption Efficiency at a certain height z(CSAE. z) expressed in %, which is the ratio of the values for CSAC 0and CSAC z.

If two materials are combined (such as the first being used asacquisition/distribution material, and the second being used as liquidstorage material), the CSAC value (and hence the respective CSAE value)of the second material can be determined for the CSDH x value of thefirst material.

Teabag Centrifuge Capacity Test (TCC Test)

Whilst the TCC test has been developed specifically for superabsorbentmaterials, it can readily be applied to other absorbent materials.

The Teabag Centrifuge Capacity test measures the Teabag CentrifugeCapacity values, which are a measure of the retention of liquids in theabsorbent materials.

The absorbent material is placed within a “teabag”, immersed in a 0.9%by weight sodium chloride solution for 20 minutes, and then centrifugedfor 3 minutes. The ratio of the retained liquid weight to the initialweight of the dry material is the absorptive capacity of the absorbentmaterial.

Two litres of 0.9% by weight sodium chloride in distilled water ispoured into a tray having dimensions 24 cm×30 cm×5 cm. The liquidfilling height should be about 3 cm.

The teabag pouch has dimensions 6.5 cm×6.5 cm and is available fromTeekanne in Dusseldorf, Germany. The pouch is heat sealable with astandard kitchen plastic bag sealing device (e.g. VACUPACK2 PLUS fromKrups, Germany).

The teabag is opened by carefully cutting it partially, and is thenweighed. About 0.200 g of the sample of the absorbent material,accurately weighed to +/−0.005 g, is placed in the teabag. The teabag isthen closed with a heat sealer. This is called the sample teabag. Anempty teabag is sealed and used as a blank.

The sample teabag and the blank teabag are then laid on the surface ofthe saline solution, and submerged for about 5 seconds using a spatulato allow complete wetting (the teabags will float on the surface of thesaline solution but are then completely wetted). The timer is startedimmediately. After 20 minutes soaking time the sample teabag and theblank teabag are removed from the saline solution, and placed in aBauknecht WS130, Bosch 772 NZK096 or equivalent centrifuge (230 mmdiameter), so that each bag sticks to the outer wall of the centrifugebasket. The centrifuge lid is closed, the centrifuge is started, and thespeed increased quickly to 1,400 rpm. Once the centrifuge has beenstabilised at 1,400 rpm the timer is started. After 3 minutes, thecentrifuge is stopped.

The sample teabag and the blank teabag are removed and weighedseparately.

The Teabag Centrifuge Capacity (TCC) for the sample of absorbentmaterial is calculated as follows:

TCC=[(sample teabag weight after centrifuging)−(blank teabag weightafter centrifuging)−(dry absorbent material weight)]÷(dry absorbentmaterial weight).

Also, specific parts of the structures or the total absorbent articlescan be measured, such as “sectional” cut outs, i.e. looking at parts ofthe structure or the total article, whereby the cutting is done acrossthe full width of the article at determined points of the longitudinalaxis of the article. In particular, the definition of the “crotchregion” as described above allows to determine the “crotch regioncapacity”. Other cut-outs can be used to determine a “basis capacity”(i.e. the amount of capacity contained in a unit area of the specificregion of the article. Depending on the size of the unit area(preferably 2 cm by 2 cm) the defines how much averaging is takingplace—naturally, the smaller the size, the less averaging will occur.

Ultimate Storage Capacity

In order to determine or evaluate the Ultimate Design Storage Capacityof an absorbent article, a number of methods have been proposed.

In the context of the present invention, it is assumed, that theUltimate Storage Capacity of an article is the sum of the ultimateabsorbent capacities of the individual elements or material. For theseindividual components, various well established techniques can beapplied as long as these are applied consistently throughout thecomparison. For example, the Tea Bag Centrifuge Capacity as developedand well established for superabsorbent polymers (SAP) can be used forsuch SAP materials, but also for others (see above).

Once the capacities for the individual materials are known, the totalarticle capacity can be calculated by multiplying these values (in ml/g)with the weight of the material used in the article.

For materials having a dedicated functionality other than ultimatestorage of fluids—such as acquisition layers and the like—the ultimatestorage capacity can be neglected, either as such materials do in facthave only very low capacity values compared to the dedicated ultimatefluid storage materials, or as such materials are intended to not beloaded with fluid, and thus should release their fluid to the otherultimate storage materials.

Density/caliper/basis Weight Measurement

A specimen of a defined area such as by cutting with a sample cutter isweighed to at least 0.1% accuracy. Caliper is measured under an appliedpressure of 550 Pa (0.08 psi) for an test area of 50 mm diameter. Basisweight as weight per unit area expressed in g/m2, caliper expressed inmm @ 550 Pa pressure, and density expressed in g/cm3 can be readilycalculated.

What is claimed is:
 1. Absorbent article comprising a fluid distributionmember having a Capillary Sorption Absorption Height for 50% of itscapacity at 0 cm (CSAH 50), further having a permeability at 100%saturation k(100), further having a permeability at 50% saturationk(50), further comprising a first fluid storage member in liquidcommunication with said fluid distribution member, said first fluidstorage member having a Capillary Sorption Absorption Height for 50% ofits capacity at 0 cm (CSAH 50), characterized in that said fluiddistribution member has a permeability at 50% of its saturation k(50)which is more than about 14% of k(100), and in that said first fluidstorage member has a CSAH 50 which is higher than the CSAH 50 of thefluid distribution member.
 2. Absorbent article according to claim 1,wherein the first fluid storage member has a CSAH 50 of more than about15 cm.
 3. Absorbent article according to claim 2, wherein the firstfluid storage member has a CSAH 50 of more than about 23 cm. 4.Absorbent article according to claim 3, wherein the first fluid storagemember has a CSAH 50 of more than about 27 cm.
 5. Absorbent articleaccording to claim 4, wherein the first fluid storage member has a CSAH50 of more than about 30 cm.
 6. Absorbent article according to claim 5,wherein the first fluid storage member has a CSAH 50 of more than about47 cm.
 7. Absorbent article according to claim 1, wherein the Fluiddistribution member has a k(50) value of more than about 18% of k(100).8. Absorbent article according to claim 7, wherein the Fluiddistribution member has a k(50) value of more than about 25% of k(100).9. Absorbent article according to claim 8, wherein the fluiddistribution member has a k(50) value of more than about 35% of k(100).10. Absorbent article according to claim 1, wherein the fluiddistribution member has a permeability at 30% of its saturation k(30)which is more than about 3% of k(100).
 11. Absorbent article accordingto claim 10, wherein the fluid distribution member has a k(30) value,which is more than about 5% of k(100).
 12. Absorbent article accordingto claim 1, wherein the fluid distribution member has a CSDH 50 value ofless than about 150 cm.
 13. Absorbent article according to claim 12,wherein the Fluid distribution member has a CSDH 50 value of less thanabout 100 cm.
 14. Absorbent article according to claim 13, wherein theFluid distribution member has a CSDH 50 value of less than about 75 cm.15. Absorbent article according to claim 14, wherein the Fluiddistribution member has a CSDH 50 value of less than about 50 cm. 16.Absorbent article according to claim 1, wherein the fluid distributionmember comprises an open celled foam.
 17. Absorbent article according toclaim 16, wherein the fluid distribution member expands upon wetting.18. Absorbent article according to any of claim 16, wherein the fluiddistribution member re-collapses upon loosing liquid.
 19. Absorbentarticle according to claim 1, further characterized in that said firstfluid storage member comprises a hydrophilic, flexible polymeric foamstructure of interconnected open-cells.
 20. Absorbent article accordingto claim 19, further characterized in that said first fluid storagemember expands upon wetting.
 21. Absorbent article according to claim20, whereby said first fluid storage member re-collapses upon loosingliquid.
 22. Fluid handling member according to claim 21, whereby saidhydrophilic, flexible polymeric foam has a capillary collapse pressureas defined herein of at least about 15 cm.
 23. Absorbent articleaccording to claim 1, further comprising a second liquid storage region,whereby both liquid storage regions are in liquid communication withsaid fluid distribution member.
 24. Absorbent article according claim23, wherein at least one of said liquid storage regions comprisesmaterial exhibiting a Capillary Sorption Absorption Height at 50% of itsmaximum capacity (CSAH 50) of at least about 40 cm.
 25. Absorbentarticle according to claim 1, further comprising a crotch region and oneor more waist regions, whereby said crotch region has a lower ultimatefluid storage capability than said one or more waist regions together.26. An absorbent article according to claim 25, wherein said crotchregion has an ultimate fluid storage basis capacity of less than 0.9times the average ultimate fluid storage basis capacity of the absorbentcore.
 27. An absorbent article according to claim 26, wherein saidcrotch region has an ultimate fluid storage basis capacity of less than0.5 times the average ultimate fluid storage basis capacity of theabsorbent core.
 28. An absorbent article according to claim 27, whereinsaid crotch region has an ultimate fluid storage basis capacity of lessthan 0.3 times the average ultimate fluid storage basis capacity of theabsorbent core.
 29. An absorbent article according to claim 25, whereinsaid crotch region has a sectional ultimate fluid storage capacity ofless than 49% of the total core ultimate fluid storage capacity.
 30. Anabsorbent article according to claim 29, wherein said crotch region hasa sectional ultimate fluid storage capacity of less than 41% of thetotal core ultimate fluid storage capacity.
 31. An absorbent articleaccording to claim 30, wherein said crotch region has a sectionalultimate fluid storage capacity of less than 23% the total core ultimatefluid storage capacity.
 32. An absorbent article according to claim 25,further characterised in that at least 50% of the area of said crotchregion contain essentially no ultimate storage capacity.
 33. Anabsorbent article according to claim 25, further characterised in thatless than 50% of said ultimate storage capacity are positioned forwardlyfrom the crotch zone in the front half of the article, and more than 50%of said ultimate storage capacity are positioned in the rear half of thearticle.
 34. An absorbent article according to claim 33, wherein lessthan 33% of said ultimate storage capacity are positioned forwardly fromthe crotch zone/in the front half of the article, and more than 67% ofsaid ultimate storage capacity are positioned in the rear half of thearticle.
 35. An absorbent article according to claim 1, furthercharacterized in that it comprises an ultimate liquid storage materialproviding at least 80% of the total ultimate storage capacity of theabsorbent core.
 36. An absorbent article according to claim 32, furthercharacterized in that comprises a ultimate liquid storage materialproviding at least 90% of the total ultimate storage capacity of theabsorbent core.